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PRESTWICH 



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ORIGIN OF THE CHESIL BANK. 







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ON THE 



ORIGIN OF THE CHESIL BANK. 



THE KELATION OF THE EXISTING BEACHES TO PAST 

GEOLOGICAL CHANGES INDEPENDENT OF THE 

PEESENT COAST ACTION. 






By JOSEPH PKESTWICH, M.A., F.K.S., V.P.G.S., 

Assoc. Inst. C.E., 
Professor of Geology in the University of Oxford. 

WITH AN ABSTRACT OF THE DISCUSSION UPON THE PAPER. 



EDITED by 

JAMES FORREST, Assoc. Inst. C.E. 

SECBETAItY. 



By permission of the Council. 

Excerpt Minutes of Proceedings of The Institution of Civil Engineers, 

Vol. xl. Session 1874-75.— Part ii. 



LONDON : PRINTED BY WILLIAM CLOWES AND SONS, 

STAMFORD STREET AND CHARING CROSS. 

1875. 

[The right of Publication and of Translation is reserved.^ 



ADVERTISEMENT. 



The Institution is not, as a body, responsible for the facts and 
opinions advanced in the following pages. 



THE INSTITUTION OF CIVIL ENGINEERS. 



February 2, 1875. 

THOS. E. HAERISON, President, 
in the Chair. 

The following Candidates were balloted for and duly elected : — 
Kennett Bayley, Eichard Frederick Church, Alfred Holt, 
Lindley William Paynter, and William Spooner Till, as Members ; 
Harry Anstey, Albert Otto Bieber, Benjamin Biram, Frank 
Charles Black, William Joseph Brown, Charles Burton, Fran- 
cisco Correia de Mesquita Cardozo, Stud. Inst. C.E., Charles 
Eckersley Daniel, Edward George Da vies, St. John Vincent Day, 
Frederic Eliot Duckham, James Kichard Fletcher, Stud. Inst. 
C.E., Frederick Flood, M.A., Philip Affleck Fraser, Joseph Jones 
Gardiner, Stud. Inst. C.E., James Hart, Edward Hedley, Henry 
Percy Holt, Henry Irwin, Charles Jones, John Alfred Jones, 
John Hunter Jones, Stud. Inst. C.E., Edward Baldwin John Knox, 
Thomas William Large, William Longworth, Niel McDougall, 
Cathcart William Methven, Frederick Ernest Muntz, B.A., 
Edmund Olander, Joseph Salter Olver, John Pagan, George 
Edward Page, Stud. Inst. C.E., Frederick Pattison, Herbert 
George Hammond Spencer, Lionel Swift, and James Honiball 
Tozer, as Associates. 

It was announced that the Council, acting under the provisions 
of Sect. III., CI. VII., of the Bye-Laws, had transferred Alfred 
Mountain Fowler and Eobert Vawser, from the class of Associate 
to that of Member. 

Also, that the following Candidates, having been duly recom- 
mended, had been admitted by the Council, under the provisions 
of Sect. IV. of the Bye-laws, as Students of the Institution: — 
Percy Rusken Allen, Francis Henry Deacon, Henrjt Eobert 
Howells Martin, Oliver Stainton Pilkington, Arthur Wilson, 
and Edmund Richard Window. 



b 2 



MINUTES OF PROCEEDINGS. 



No. 1,403. — " On the Origin of the Chesil Bank, and on the Relation 
of the existing Beaches to past Geological Changes independent 
of the present Coast Action." By Joseph Prestwich, M.A., 
F.E.S., V.P.G.S., Assoc. Inst. C.E. 1 

In a valuable Paper on the state and origin of this bank, 2 read 
before the Institution in 1853, Mr. (now Sir John) Coode remarks : 
" There are few subjects of greater professional interest, than the 
accumulation and travel of shingle, since the very existence of 
many harbours depends, in a great degree, upon a correct under- 
standing and judicious application of the laws which govern its 
movement; and without a knowledge of these, it is impossible to 
devise such measures as may with confidence be adopted, either to 
assist its progress, direct its course, or to remove accumulations 
that may have taken place." 

It is with a view to aid in the solution of the problem that the 
Author brings before the Institution some fresh geological evidence 
which has led him to form an opinion upon the origin of the 
Chesil Bank different to that arrived at by this eminent engineer. 
(Plate 3.) 

Sir John describes this remarkable bank as " a vast mound of 
shingle, in the form of a narrow isthmus, lying upon the western 
seaboard of Dorsetshire, between Abbotsbury and Portland ; its 
general direction or bearing is south-east, and its length is 
10 j miles. Commencing at Abbotsbury Castle (to the westward of 
which the shingle slopes down from the low cliffs, as in the case of 
an ordinary beach) the Bank skirts along the margin of the 
meadows, for half a mile, when it meets ' The Fleet' or ' Backwafer,' 
a shallow estuary varying from a quarter to half a mile in width ; 
it then runs parallel to the general line of the mainland as far as 
Wyke, a distance of eight miles ; from this point, the Bank takes 
a more southerly direction, until it joins the Peninsula, or what 
is more commonly called the Island, of Portland, when it again 
assumes the character of an ordinary beach." 3 That the pebbles of 



1 The discussion upon this Paper occupied portions of three evenings, but an 
abstract of the whole is given consecutively. 

2 Vide Minutes of Proceedings Inst. C.E., vol. xii., p. 520 ; " Description of the 
Chesil Bank, with remarks upon its origin, the causes which have contributed 
to its formation, and upon the movement of Shingle generally,'' by John Coode, 
M. Inst. C.E. See also Mr. J. E. Redman's Papers on the South and East Coasts, 
and the discussion thereon, vol. xi., pp. 201-4, and vol. xxiii., pp. 226-56. 

3 Ibid., vol. xii., p. 521. 



ON THE ORIGIN OF THE CHESIL BANK. 

this great beach decrease in size from Portland to Abbotsbury 
has been long a matter of observation. At the former end they 
may, as a whole, be considered as flattened ovoids 3 inches to 
4 inches across, and at the latter as small spheroids of £ inch to 
1 inch in diameter. 

The average width of its base at the level of low water of 
ordinary spring tides at the Portland end was ascertained by Sir 
John Coode to be 200 yards, and its height 42 feet 9 inches above 
high water of ordinary spring tides, and at the Abbotsbury end 
170 yards wide and 22 feet 9 inches high; and while at the 
former place it extends to a depih below high water of 48 feet, at 
the latter it only reaches 36 feet. Beyond Abbotsbury the beach 
joins the shore and slopes up to the low cliffs, and the depth below 
water to which the shingle descends gradually decreases to 21 feet 
at Burton Cliff; while 2 miles farther, at Bridport harbour, it only 
extends to a depth of 9 feet. It was likewise proved that the 
beach rested against a shelf of Kimmeridge Clay, which rose on 
the east side of the bank to from 3 feet to 4 feet above low-water 
spring tides. The Paper contains other important information re- 
specting the slopes of the bank, the depths off it, the set and 
velocity of the tides, the direction of the winds, the distribution 
of the shingle, and the action of the waves. 1 

Incidental notices 2 had before been given of the composition 
of the shingle, but Sir John was the first to make an ex- 
haustive examination. He describes it as composed " chiefly, 
of chalk flints, with a small proportion of pebbles from the red 



1 Among others who have written on the Chesil Bank and on the origin of the 
Fleet may be mentioned: De la Beche, "Geological Observer," p. 65; Godwin- 
Austen, " Quarterly Journal Geol. Soc," vol. vi. ; Lyell, " Principles,'' 10th ed., 
vol. i., p. 531 ; Her^chel, " Physical Geography," p. 91 ; Greenwood, " Rain and 
Rivers," pp. 119, 132, and "Geological Magazine," vol. vi., p. 523; Bristow and 
Whitaker, " Geological Magazine," vol. vi., pp. 325, 133 ; Codrington, ibid.,vol. vii., 
p. 23; Fisher, ibid., vol. x., p. 4S1 ; Mellard Beade, ibid., vol. x., p. 573; Pen- 
gelly, " Transactions of the Devonshire Association," vol. iv., p. 195. The Author 
ha I not at the time of writing this Paper seen the several further notices, mostly 
by the same writers, together with Mr. Kinahan, in the volume of the " Geological 
Magazine" for 1871 (New Series, Decade II., vol. i.). The Chesil Bank is 
generally regarded by them from the same point of view as Sir John Coode. 
The origin of the Fleet is, however, more especially treated of in these 
Papers. 

2 Mr. Godwin-Austen. F.R.S., in his Paper "On the valley of the English 
Channel," which contains much valuable information relative to the distribution 
of the shingle over its area, remarks that, "On the Chesil beach may be collected 
pebbles of limestone, greenstone, trap, and old red sandstone, derived fiom the 
older rocks of South Devon."—" Quarterly Journal Geo]. Soc," vol. vi. (1819> p. 73. 



6 MINUTES OF PROCEEDINGS. 

sandstone, some of these being of a dull-red colour, others of a 
brown, or dull yellow, with occasional red marks resembling blood- 
spots. A peculiar kind of jasper pebble, with flesh-coloured red 
predominating, is not very uncommon : these have sometimes been 
mistaken for Devonshire limestones, to which many of them bear 
a great resemblance ; they do not, however, contain any calcareous 
matter, as there is not the slightest effervescence on the application 
of muriatic acid. There are also, occasionally, pebbles which are 
decidedly porphyritic, both green and red ; they are comparatively 
rare, but nevertheless are found in sufficient numbers to prove, that 
their presence is duo to something more than accidental causes." 1 

It was evident from this that the bulk of the shingle was de- 
rived not from local rocks, but from others at a distance. With 
the view to ascertain the source of these, an examination of the 
geological structure of the coast from Portland to Start Foint 
was instituted by Sir John, who found that neither the Portland 
rocks nor any of the strata of the Jurassic series, which extend 
from Portland to L}'ine Regis, could furnish materials corre- 
sponding in character with the shingle of the beach ; but that 
between Lyme and Axmouth beds of "chalk with numerous flints" 
cap the cliffs, and are still more developed at Beer Head, ex- 
tending in places to near Sidmouth, which could " have afforded 
a considerable supply of flints." Further, at Sidmouth, the New 
Red Sandstone commences and extends westward past Budleigh 
Salterton, where " the beach is almost entirely composed of 
pebbles of precisely the same kind as those previously described " 
as occurring in the C'hesil Bank. Upon this beach also were 
found the jasper pebbles which were traced to Aylesbere Hill, 
<i miles inland. The pebbles of porphyry were referred to the 
lleavitree conglomerates, or to those which crop out on the coast 
between Beer and Torbay. 

The conclusion he arrived at was, " that the only possible source, 

from which the shingle of the Chesil Bank can have been derived, 

is between Lyme Regis and Sidmouth," and that it is propelled 

eaJ^ti, -westward along the coast by the action of wind-waves and the 

heavy seas due to the prevalent and .strongest winds. 

In the accuracy of this description the Author, in the main, quite 
agrees, with some additions afterwards to be mentioned. He also 
admits that a considerable portion of the shingle is identical in cha- 
racter with materials existing in the strata of the West Dorset and 
Devonshire coasts ; but he does not consider that the shingle has tra- 



1 VOL Minutes of Proceedings In. t. O.E., vol. \ii., p 



ON THE ORIGIN OF THE CHESIL BANK. ' 

veiled directly from the cliffs between Budleigh Salterton, Sidmouth, 
and Lyme Begis, and so eastward along the coast to the Chesil Bank. 

The latter view involves the anomaly that the largest shingle is 
found at the Portland end of the beach, or at the most distant 
point from which it had travelled. This did not escape the atten- 
tion of Sir John Coode, who suggests that the reason why " the large 
shingle is always thus found ' to leeward,' " is that, " as a rule, 
the large pebbles move more readily than the small, however para- 
doxical this may appear;" and he accounts for this on the suppo- 
sition that, practically, the larger pebbles are more exposed than 
the smaller ones to the action of the waves. It seems, however, to 
the Author, as it did at the time to the Astronomer Boyal, that 
this decrease in the size of the pebbles from Portland to Abbots- 
bury and Burton is a serious objection to their travel along the coast 
from the westward. The Author is further of opinion that, with an 
easterly movement of the shingle, there could not be that constant 
increase in the dimensions of the bank, as it trends towards Port- 
land, without a discharge of the overloaded end into the East Bay. 
He will attempt to show, on the contrary, that the Chesil Bank 
is formed by the accumulation of shingle derived from the south 
end of Portland and from the sea bed westward thereof, and that 
the movement of the beach is north-westward. 

Although the beach has often been described, and is well known 
to consist chiefly of Chalk flints with the subordinate Devon- 
shire pebbles before referred to, two other essential elements 
seem to have escaped notice. The one is the common occur- 
rence of pebbles of Greensand chert, and the other of pebbles, 
often subangular, of the dark Portland-stone flint, together with a 
very few pebbles of the harder limestones and oolites of Port- 
land. Both these have been found, although in very small spe- 
cimens, as far northward as Abbotsbury. The Portland rock spe- 
cimens clearly indicate their origin ; and it will now be shown that 
all the other materials have also their source from the same 
direction. For, although there can be no doubt that originally 
many of the beach pebbles are derived from Devonshire rocks, yet 
it is probable their transport to Portland is not due to any existing 
agency, but to causes in operation at the end of the glacial period 
and before the land had assumed its present position and shape. 

At that period the south coast of England was less elevated than 
it now is. It was fringed by a beach, remnants of which are yet 
visible at many places round the coast, from the Bristol Channel to 
Brighton, which by a subsequent change of level has been raised to 
various heights above the present shore, — for example, to 14 fee 



8 MINUTES OF PROCEEDINGS. 

above the existing beach, at Brighton, 25 feet to 30 feet in Torbay, 
35 feet at Plymouth, and 10 feet at Falmouth. 

The Eaised Beaches, like the existing beaches, are composed very 
largely of local materials, with others in addition derived from a 
distance. They follow also closely the present coast line, ex- 
cepting where, from the softer nature of the rocks, the amount 
of wear by the sea has been great, and has formed more deeply 
indented bays than previously existed. These beaches are of 
frecpient occurrence among the hard rocks of the Devonshire 
cuast from Plymouth to Torquay ; but where the rocks are more 
yielding, and the denudation consequently has been greater, the 
coast has been worn back and the old beaches removed. No 
traces of them have been detected between the mouth of the Exe l 
and Portland, though such beaches have been long known farther 
eastward, — at Selsea, Brighton, and elsewhere. One of these rem- 
nants, of some extent, has within the last few years been discovered 
at the Bill of Portland. This " raised beach" was first noticed by 
Mr. Bristow, and then briefly described in 1852 by Mr. Weston, 2 who, 
however, merely stated that it was formed of " beach-pebbles (with 
a few chalk-flints)." It has been several times mentioned 3 since ; 
but the foreign element seems to have escaped notice, excepting one 
portion of it by Messrs. Pengelly andVicary .* The Author visited the 
beach in 18G3, and again in the summer uf 1873, when he had an 
opportunity of studying it more at leisure. 5 It extends a distance 
of 1 mile from the landmark at the Bill to the sand-holes near 
('< odn< ire Point on the east, and ^ mile northward from the landmark 
on the west side, ranging inland apparently i mile, and covering 
about 100 acres. On the east side it is thin and sandy; at the 
Bill it attains a thickness of 4 feet to 5 feet, which farther west- 



1 Mr. Godwin-Austen shows reason for believing that the sea extended some 
distance up the valley of the Exe — " Quarterly Journal Geol. Soc.," vol. vi. 
(1849), p. 91. 

- Vide " Quarterly Journal Geol. Sue.," vol. viii.. p. 117. 

3 It. Godwin- Austen, " Quarterly Journal Geol. Soc," vol. xiii. (1855), p. 41. 
WMtaker, "Geol. Mag.," vol. vi. (1869), p. 4:JS. 

4 Mr. Pengelly thus describes the beach: "Flints were the staple of the 
deposit, but Budleigh Salterton pebbles were quite as prevalent as on the Chesil 
Bank. As a whole tiny were somewhat smaller; nevertheless, we found one 
specimen in the aucienj beach much larger than any we had Been on the modern 
one. We extracted one granitoid pebble containing a large amount of schorl, and 
without doubt of Dartmoor derivation. Sand was much more abundant than on 
any part of the Chesil Bank we visited. The basal portion of the accumulation 
consisted of angular, subangular, and rounded blocks of the rock of the immediate 
locality." — " Trans. Devon. Assoc. Be. Lit. and Art.," vol. iv. (1S71), pp. 201-2. 

5 Vide "Quarterly Journal Geol, S c," vol. xxxi, p. :;:J. 



ON THE ORIGIN OF THE CHESIL BANK. V 

ward increases in places to as much as 8 feet to 10 feet, where it 
forms a thick and compact bed of well-rolled shingle. At the 
Bill, the base of the old beach is only 21 feet above the top of the 
present beach ; but it rises to a height of 32 feet at the north-east 
end, and of 47 feet at the north-west end. At places it has been 
cemented by calcareous springs into a hard conglomerate, though 
generally, especially at the west side, it presents a loose shingle, 
exactly like an existing beach. Fig. 1 is a section where it caps 
the cliff near the Bill. (See Plate o.) 

Fig. 1. Section of the " Raised Beach," Portland Bill. 










a. Raised beach. 

b. Cliff of Portland stone. 

c. Present beach. 

The pebbles, of which the raised beach consists, vary in size on an 
average from 2 inches to 4 inches in longest diameter, with a few of 
larger dimensions. They are, on the whole, larger on the west than 
on the east side, and consist chiefly of chalk flint, greensand chert, 
the harder oolites, limestones, and black flint of the local Portland 
and Purbeck strata, with a not inconsiderable number of pebbles 
of red sandstone, of light reddish coloured and grey quartzites, of 
light and dark red porphyry, slate, micaceous grey sandstone or 
grit, and white and red quartz ; with these the Author found one 
largish subangular pebble of reddish granite. The extraneous 
pebbles may be referred to the following formations 1 : — 

Extraneous Pebbles nccurrinsr in the Rocks from which the Pebbles 

Shingle of the Raised Beach. are derived. 

Flint (I.) Chalk. 

Chert (2.) TJprER Greensand. 

Red and purple sandstone . j (3.) The New Red Sand- 
Red, grey, and white quartzite > stone and Conglome- 

Porphyry ) rates of Devonshire. 

Slate, grit, and quartz . . . . (4.) Devonian Series (?) 

Granite (5.) Cornwall? Darimoor. 

1 Some portion may probably be referred to tbe old flint gravel capping 
Blackdown Hill, carried down by former streams. In this gravel tbeie are also 
a few small pebbles of jasper.— " Quart, rly Journal Geol. Sor.," vol. xxxi., p. 41. 



10 MINUTES OF PROCEEDINGS. 

The Chalk and Greensand como to the coast at White Nore, 
6 miles east of Portland, and again at Axmouth, 30 miles west of 
Portland. The pebbles of these rocks afford, therefore, no sufficient 
clue to the direction from whence they were drifted ; l but the 
quartzites and porphyries point unmistakably to a westward or 
Devonshire origin. The evidence of the quartz-veined sandstone 
and quartz pebbles is only rather less decisive ; but the origin 
of the granite pebble has not yet been ascertained. It may 
possibly come from East Cornwall. 

In order to obtain some corroboration of this opinion, more 
particularly on the specimens other than the Budleigh Salterton 
pebbles, they were submitted to two geologists thoroughly well 
acquainted with the rocks of their respective counties. Mr. Hen- 
wood, F.B.S., of Penzance, cannot identify any of the porphyries 
with Cornish rocks. Only the one specimen, No. 5, of grey sand- 
stone with quartz veins, bears some resemblance to a rock which 
occurs between Liskeard and Looe. Of the granite pebble he says 
" that patches, though small ones, of a similar rock occur here 
and there in the great central range which extends from Gram- 
pound to Lanlivery and St. Columb ; but this granite does not 
reach the coast," and he considers its origin uncertain. Mr. 
Yicary, F.G.S., of Exeter, observes of the porphyries and quartz- 
ites, " They are familiar to me, and I think I could probably 
find their counterparts either in our gravel beds on the slopes of 
the Exe, or in the New Eed Sandstone conglomerate at Dawlish. 
Two of the pebbles I consider identical with the Budleigh Tied." 
Beferring to some additional specimens, Mr. Vicary remarks, 
" Their identity (with the Budleigh Salterton quartzites) cannot 
be doubted ; the specimens from both places containing the same 
fossil tubes (annelids), and are otherwise alike." The granite he 
could not identify. Mi - . Yicary afterwards sent a counterpart 
series from Devonshire, which are submitted to the Institution, 
together with the Portland specimens. They leave no doubt 
of the identity of the two series, and that the Bed Sandstones 
and conglomerates of Devonshire furnished the materials for a 
portion of the pebbles in the raised beach. 2 

That the general movement of the shingle along the coast at 

1 Streams may have brought Some of these from the north, as the rivers flowed 
then as now from north to sooth, fur a drift bed on the summit of Portland ooa> 
tains pebbles and blocks of tertiary sandstone, pebbles of chalk, flint, and of 
greensand chert, all of which come from formations between Weymouth and 
Dorchesti r. 

2 Part of the flint and chert pebbles may he derived frnm the chalk and 
greensand to the westward, but it is possible, aud perhaps moro probable, that a 



ON THE ORIGIN OF THE CHESIL BANK. 1 1 

this former period was, as at present, from west to east, is cor- 
roborated by other facts. Pebbles of old crystalline rocks are 
found in the " raised beach " of Brighton, 1 and granite pebbles in 
shingle of the same age at Hove. 2 Similar specimens occur in 
synchronous deposits in Bracklesham Bay. 3 More recently " a 
block of indubitable Portland fossil wood " 4 has been found on the 
shore at Selsey, derived, in all probability, from the old shingle. 
Mention has also been made of the occurrence of silicified wood 
at Hove derived from the Upper Greensand farther west, and of 
rolled fragments of silicified coral at Hastings, Hove, Ryde, and 
Sandown, which may have had the same origin or have come from 
the Portland oolite 5 during the old beach time. It need scarcely 
be stated that no formations older than the Cretaceous and the 
Wealden series occur eastward of the Isle of Wight. 

Mr. Godwin-Austen, however, records a fact which may appear to 
militate against this conclusion. After noticing that the marginal 
movement of the shingle at present is taking place in a direction 
from west to east, he says that during the accumulation of the 
raised beaches it was the very reverse way — from east to west. 6 This 
opinion is, however, founded solely on the circumstance, that the 
raised beaches at Slapton and elsewhere on the Devonshire coast 
contain subangular fragments of chalk flints, whereas no chalk 
exists in situ anywhere westward of Sidmouth. But these flints are 
not, accompanied by the debris of any of the other formations, which 
lie also to the eastward ; and although the chalk is not in situ in 
West Devon, old gravels at high levels contain chalk flints, whence 
the supply of flint pebbles may have been derived by the agency 
of streams passing through those districts. 7 



considerable quantity of these were carried into the old sea by streams from the 
northward, otherwise it is likely that the proportion of chert and new red 
sandstone pebbles would have been larger. 

1 Mantell's " Geology of the South-East of England," p. 32. 

2 Murchison, " Quarterly Journal Geol. Soc," vol. vii. (1851), p. 306. 

3 Dixon's "Geology of Sussex," p. 14. Mr. Godwin-Austen mentions also tho 
occurrence of pebbles of granite, porphyry and other old and crystalline rocks, 
but suggests that they may have been derived from the waste of a subjacent bed. 
" On the Newer Tertiary Deposits of the Sussex Coast," '• Quarterly Journal 
Geol. Soc," vol. xiii. (1857), p. 62. 

4 The Rev. O. Fisher in " Geol. Mag.," vol. viii., p. 524. 
s Mr. Perceval, ibid., vol. viii., pp. 476 and 576. 

6 " On the Valley of the English Channel." — " Quarterly Journal Geol. Soc," 
vol.vi. (1849;, pp. 87 and 88. 

7 Other such outliers probably extended farther westward, and have been 
destroyed by subsequent denudation, which is known to have been considerable 
since that period. Ou this subject Mr. Pengelly, speakiug of the occurrence of 



12 MINUTES OF PROCEEDINGS. 

There is, however, from all the other facts, every reason to helieve 
that the shingle at the period of the " raised beaches " travelled from 
west to east, and that this was due chiefly 1 to the action of the 
prevailing winds ; fur a certain proportion of the shingle of the 
" raised beach" at the Portland Bill consists of pebbles derived 
from the Devonshire rocks, carried, in all probability, in the ordi- 
nary way by wave-action along a more direct line of coast than 
now exists. 

The conditions have since materially changed. Of the old 
coast only a few advanced points exist, the sea having, where 
the strata are softest, gained on the land and formed deep 1 lays, 
which have modified the direction of the shingle of the present 
period. 

It results from this destruction of old coast lines, that a quantity 
of shingle derived from the old beaches must, owing to its inde- 
structible character, be spread over the bed of the Channel. 

Further the raised beaches are observed to be almost always 
covered by a peculiar local deposit consisting of angular rubble, 
derived from the adjacent inland strata, often of very great thickness. 
At Portland Bill only traces of it exist, but at the north end of the 
beach it is from o feet to 10 feet thick ; at Chesilton a synchronous 
deposit is 60 feet thick, and at Brighton it attains a thickness of 
70 feet to 80 feet. In the chalk districts it consists largely of 
sharp flint debris. The quantity of this material, which often far 
exceeds that of the beach itself, must have added largely to the 
Channel shingle : while frequently a third and still larger source 
of supply to the present beaches has been the flint gravels which 
occur on the south coast. 

It is commonly supposed that the flint shingle of the beaches of 
the south of England is chiefly derived from the destruction of the 
chalk cliffs, and the wearing down of the contained flints. .Such, 
however, is far from being the only, or even the main, source of 
supply. The great bulk of the flint shingle is derived from the beds 



flints in the " raised beaches," at Slapton, near Start Point, says that there is a 
fatnl objection to the flints having travelled beyond Budleigh, or any more 
easterly district, in the fact that "there are comparatively few flints on the 
numerous beaches between Budleigh and Slapton." On the other hand, he states 
that there are gravels with Hints a few miles inland from Torquay, as well as in 
fissures and pock) is on many heights in that and other localities, "the relics of 
a wide-spread gravel which once covered the district generally." "Trans. Devon. 
Assoc.,' 1867, pp. 4 and 5; and op. cit., p. 2l)4. 

1 This is Dot the place to discuss the geological question, but there is reason 
to believe that at this period ice-action aided in the transport of the shingle. 



uN THE ORIGIN OP THE CHESIL BANK. 13 

of gravel which fringe the coast in many low-lying districts, and 
which cap the hills in other places. Even in beaches fronting the 
chalk cliffs, the proportion of flints derived from the cliffs to those 
derived from the gravel beds is generally small, as for example in 
the beach under the chalk cliffs west of Beachy Head, at Brighton, 
and at the White Nore ; while on the beaches of Folkestone, 
Hastings, Worthing, Christchurch, and Weymouth, the shingle 
is almost entirely composed of old flint-gravel (the flints of course 
derived originally from the chalk), with a comparatively small 
number of chalk flints. The difference of origin of the flints is 
readily seen. Those from the chalk cliffs are more or less sub- 
angular, their worn angles showing a black interior, and the other 
parts, where the original surface or coating of the flint has been 
preserved, are white. On the other hand, those from the gravel, 
which are likewise subangular — though generally more, and more 
uniformly, worn — are also black in the centre, but with a thicker 
discoloured crust, having the yellow or brown stain they acquired 
in the gravel bed. Thus the one pebble is black and white, and 
the other black, white, yellow, and brown. 

In fact, the beaches at Dover, Eastbourne, Brighton, and on the 
coasts of Hants and Dorset owe little to their chalk cliffs, but are 
due almost entirely to the great beds of gravel which range 
down the several main river valleys, and cover the flat tertiary 
plains extending from Poole to Bognor and Brighton, and which 
are scattered in lesser quantities along the narrower valleys at the 
foot of the North and of the South Downs. These great trails 
and sheets of gravel constitute the primary element in the forma- 
tion of the Channel beaches. The chalk cliff element is com- 
paratively unimportant, and owing to the size of the flints derived 
directly from the chalk, and their greater angularity, they often 
remain at or near the spot on the sea bed where they were first 
left by the wearing away of the cliff. The danger to the ports on 
the south coast lies, therefore, not so much in the conspicuous and 
lofty cliffs which form so striking a feature of the landscape, but 
more in the less obtrusive plains and valleys which in places skirt 
the shore or intersect the long line of cliffs. 

The thick mass of broken chert in situ on the hills around 
Lyme, and near Abbotsbury, and the broken flints capping the 
chalk hills above Abbotsbury, at White Nore, and some of the 
higher hills of the Isle of Wight, constitute another element 
of some importance. These are less readily distinguished in the 
shingle beaches. 

The existing beach, due to the wear of the cliffs and low lands 



]4 MINUTES OF PROCEEDINGS. 

now going on, is therefore supplemented by such portions of these 
old shingles scattered over the Channel bed, which may, from their 
position, be thrown up on the present shore by the action of tidal 
currents and storm-waves. That such submarine shingle does 
exist is sufficiently recorded by the Admiralty charts and pub- 
lications," as well as by the researches of Captain Martin White 2 
and of Mr. Godwin- Austen 3 and others. (See Plate 3.) 4 

If the beach be formed on a line of open coast, it is now per- 
fectly well established that it moves in the direction of the strongest 
wind- waves ; and from the frequency and excess of force of the 
southerly and westerly winds on the south coast of England, the 
travel of the shingle is no doubt, in the main, from west to 
east. Still it is questionable whether at present any shingle from 
Cornwall and Devonshire passes eastward of Portland. 5 

The prevalent and effective winds on this coast are those from 
the S. and S.S.W. Sir John Coode, taking the mean integral effects 
of the winds at Devonport during the years 1841-3, on Whewell's 
and Osier's anemometers, recorded by Mr. W. Snow Harris, 6 adopted 
a mean of S.W. £ W. as the direction of the greatest wind-force. 
Both instruments are admittedly imperfect, but Whewell's, which 
better marks the stronger winds, gives a S.S.W. direction. And if, 
instead of the calculated result obtained with Osier's instrument, 
which gives too great a value to the weaker winds, and is there- 
fore discordant with the other instrument, the separate integral 
effect be taken of the prevalent winds from the two quarters which 
concern this inquiry, viz., those from W. and S.W., or a mean of 
W.S.W., and those from the S. and S.W., or a mean of S.S.W., it 
will be found that the greater force appertains to the latter or 
S.S.W. quarter. 

1 " The Channel Pilot." Part I., 1874. 

2 " Sailing Directions for the English Channel," 4th ed., 1850. 

3 "Quarterly Journal Geol. Sue.,'' vol. vi., op. cit. and map, p. 9G ; and vol. 
xiii. 1 1857 , p. 41. 

4 The shingle in the soundings is marked in two characters, because the x was 
inserted before it was resolved to insert the letters. 

s He would refer in particular to the Paper by Mr. Palmer (" Phil. Trans." 1834), 
also to one by Colonel Sir W. Reid (" Prof. Papers of the Corps of Royal Engineers," 
vol. ii., p. 128), in which the general eastward movement is noticed, together with 
the fact that siliceous pebbles from Devon are driven past Lyme cob, and, as 
Sir William considers, on to the Chesil Rank, but not past Portland. 

6 "Report of the British Association for the Advancement of Science," 1844, 
p. 241. The results are only given as approximative, p. 249. 



ON THE ORIGIN OP THE CHESIL BANK. 



L5 



Relative mean Integral Effect (= velocity in miles per hour x total 
number of hours) of the Winds at Devonport from the S. to S.W. and 
W. to S.W. for the two tears 1841-2.— (Compiled from Table XIV., p. 265, 
of Snow Harris's Report.) 



,,,. , Integral 
™ lnds - < Effect. 


Winds. 


Integral 
Effect. 


S. i 17,290 
S.S.W. 7,860 
S.W. ' 17,549 


W. 

W.S.W. 

S.W. 


12,52S 
6,470 
17,549 


42,699 


36,547 



The excess of the S. and S.S.W. winds is still more apparent 
when regard is paid merely to the amount, as shown in the follow- 
ing Table of the same report, which gives the actual amount of 
wind according to Whewell's anemometer. (Table IV., p. 260 and 
p. 248.) 

Mean Amount of Wind for the Three Years 1841, 1842, 1843. 



N. 


N.N.E. 


N.E. 


E.N.E. 


E. 


E.S.E. 


S.E. 


S.S.E. 


483 


419 


437 


396 


996 


134 


87 


229 


s. 


S.S.W. 


S.W. 


W.S.W. 


W. 


W.N.W. 


N.W. 


N.N.W. 


2,569 


2,582 


193 


13 


396 


476 


203 


259 



Hence it may be inferred that on this coast a mean direction of 
S.S.W. may be adopted as representing approximately that of the 
effective wind-force, even if it should not be a point more south. 

Lyme Bay forms a tolerably regular semicircle facing the south. 
The prevalent winds being off shore on the west horn of the bay, 
not much shingle travels from Torbay to the Exe. Beyond this 
river, eastward, the trend of the coast exposes it more directly to the 
action of the S. and S.W. winds, and drives the shingle from the 
Exe eastward, carrying with it the quartzite pebbles of Budleigh 
Salterton in decreasing quantity to and somewhat beyond Lyme, 
and the chert and flints of the cliffs between Sidmouth and Lyme 
to Bridport and may-be Burton. Arrived, however, off Bridport 
harbour, the trend of the coast becomes slightly southerly, and it 
is a question whether the shingle is carried in any quantity in 



16 MINUTES OF PROCEEDINGS. 

this direction beyond Burton Bradstock ; l for the wave due to a 
S.S.W. wind-force becomes parallel with the coast at Bridport, and 
the lateral propelling power ceases. Proceeding towards Abbots- 
bury, the coast takes gradually a btill more southerly trend, so that 
the wind-wave here forms with it an augle facing north-westward, 
which angle increases as the coast trends to Portland. It therefore 
follows that with the prevalent S.S.W". wind- waves the shingle of the 
Chesil Bank should travel from Portland to Abbotsbury ; and this 
is in accordance with, 1st, the smaller size of the pebbles, i'ndly, the 
lesser height and breadth of the bank itself, 3rdly, the decrease 
of the depth of the beach under water as it trends in that direc- 
tion, and, 4thly, the presence of Portland rock debris. As before 
mentioned, the sub-water beach suddenly diminishes at Burton 
from a depth of 21 feet to 9 feet. At this part of the coast the 
shingle which has travelled, in gradually decreasing quantity, from 
Portland under the influence of S.S.W. wind-waves, loses, owing 
to the changed direction of the coast, its forward movement, and 
on the other side of Bridport is met by the shingle which has 
been propelled eastward from Budleigh and Sidmouth. 2 These 
opposite movements agree also with the fact mentioned by Sir 
John Coode, that the sand to the westward of the Chesil Bank 
is derived from Charmouth, while that at the other end is derived 
from the wear of the pebbles ; and also with another fact mentioned 
by the same author as exceptional, viz., that between Black 
Is ore and Chesil ton, the beach, which there consists entirely of 
local or Portland debris, does in fact travel northward, or towards 
Chesilton where it falls into the Chesil Bank. 3 These several 
movements of the sand and shingle are, on the views here 
expressed, in keeping with and produced by the same cause. 
They all exhibit a uniform travel to the N.W., : — a movement ] 
which, commencing at and off the Bill of Portland, is continued 

1 Mr. Pengelly mentions that he and Mr. Vicary had traced the Budleigh I 
Salterton pebbles " eastward as far as Finney Bay, immediately west of Lyme 
Regis, that is 18 miles on the road to the Portland isthmus ;" but " found the 
pebbles less and less abundant as we moved eastward, until on the confines of . 
Dorset they became extremely rare." Mr. Pengelly, however, in consequence 
of the number of pebbles of Builleigh quartzites, " porphyritic trap, schorlaceous 
rock, and granite" in the Chesil Bank, adopted Sir John Coode's views of its 
origin (op. cit., p. 198, et seq.). 

• At the same time the amount of sand increases, while, according to the 
Admiralty chart, gravel or shingle is spread over many places in the bight of the 
bay at distances of 2 miles to 5 miles from the .diore. 

3 Between Portland Castle and the Ferry bridge at Wyke the shingle in the 
east side of the bank ;ilso travels in the same northward direction. 



ON THE ORIUIN OF THE CHESIL BANK. 17 

in the same direction to the point where the moving power fails. 
In the same way the wind-wave action, which propels the Devon- 
shire debris eastward, diminishes greatly in its effects at Lyme 
Eegis, and probably ceases altogether near Bridport, on either side 
of which there may be some extent of oscillation. 

That there is no beach between Black Kore and the Bill is 
easily understood ; for the tide, sweeping slowly round the West 
Bay, rushes both in flood and ebb with great velocity along this 
part of the coast, which is bounded by perpendicular cliffs, at the 
foot of which the sea rapidly deepens, — the depth at 500 yards from 
the shore being 100 feet; whereas off Chesilton this contour line is 
at a distance three times greater and the force of the current 
is much less. 

It is possible that the " raised beach " at the Bill furnishes 
directly but a small contingent of shingle to the Chesil Bank, and 
that the main source of supply lies in the materials of the sub- 
merged portions of that beach, which is spread over the sea bed off 
and to the westward of the Bill. The soundings on the Admiralty 
chart show shingle to be there present in many places, and that 
it is drifted over the depressed area excavated by the tidal current 
on the west side of Portland, where it is subject to the action of 
the Bace, here of great force, carrying it out to sea on the flood 
and inshore on the ebb tide. 

This current is clue to the circumstance that the Channel, 
112 miles wide between Plymouth and the coast of Brittany, 
becomes suddenly contracted between Portland Bill and Cap de la 
Hague to a width of 60 miles. The Channel afterwards expands 
again to a width not much short, in places, of what it had 
westward of those points, — whereby the great tidal wave, dammed 
in, as it were, between these points, and suddenly compressed and 
thrown on itself in passing by and out of Lyme Bay on one side, 
and of St. Malo Bay on the other, gives rise to the Pace of 
Portland on the English coast, and to that of Alderney off the 
French coast. The current thus created runs, for some hours each 
tide, off the Bill of Portland, — with a southward and eastward 
direction on the flood, and a westward and northward direction 
on the ebb, — with a velocity, when it attains its greatest force, of 
from 5 to 6 knots per hour. This is sufficient to move large 
gravel, for a current with a velocity of 1 foot per second suffices 
to transport fine gravel, and, of 3 feet per second, stones the size 
of an egg ; and Mr. Hopkins was of opinion that the force increases 
as the sixth power of the velocity. The surface velocity of the 
Race at its maximum exceeds 8 feet per second. But the current, 

[1874-75. N.s.] c 



18 MINUTES OF PROCEEDINGS. 

so rapid at the southern end of Portland, is reduced to 1 or It knot 
per hour off Chesilton, and although it might carry the shingle 
toward it, would not drive it on to the Chesil Bank. This is 
effected by the storms to which this coast is exposed, acting 
probably conjointly with the great tidal wave. This wave, pass- 
ing from the ocean into the shallower waters of the Channel, 
becomes a wave of translation, which under certain conditions, 
such as a rapid decrease of depth, or the narrowing of its channel, 
possesses a greater or less propelling and eroding power. Ordi- 
narily this power is very small or imperceptible; but in the 
cases under consideration circumstances combine to give it great 
effect. 

For at a distance of 25 miles south of the Chesil Bank, and parallel 
with it. is the contour line of 30 fathoms, and the line of 20 fathoms 
passes within G miles of the bank, and only 1 mile from the south 
end of Portland: while the line of 15 fathoms extends to within 
a mile of the shore oft' the northern portion of the Chesil Bank. 
This leads, during storms, to the inset of a very heavy ground- 
swell, and causes the waves to break on the bank with great 
violence. Even when there is little wind, the waves, during the 
prevalence of a ground-swell, approach the shore at, or nearly at, 
right angles. (See Plate 3.) 

The Author believes, therefore, that the shingle formed on the 
former line of coast of the " raised beach " period and now spread 
over the sea bed westward of Portland, is deflected northward by 
the influence of the Pace, and thrown up during storms on the 
south end of the Chesil Bank, together with the debris of the Port- 
land rocks between Black Nore and Chesilton. 1 

The shingle thus thrown up - is exposed to the prevalent wind- 
waves from the south and south-west. Taking as a mean a S.S.AV. 
direction, these waves form with the shore at Chesilton an angle 
of 20°, which decreases to 10° at Abbotsbury and to 6° at Burton, 
so that the lateral propelling, never large, becomes gradually 
less in proceeding to the north-west ; while at the same time the 
force of the waves diminishes in consequence of the shallowing 



' White, both in his "English Channel " and the "Admiralty Tilot Ouide," 
states that in the West Bay of Portland, in the direction of Abbotsbury, the deep- 
sea shingle is apparently cast up in small and decreasing quantity. 

7 The pebbles at the base of the Chesil Bank to a depth of 6 to 8 fathoms are 
covered with balani, but after a gale they are removed, though the original 
pebbles are there (Minutes of Proceedings tnst C.E., vol. xii., p. 534). Mr. 
Damon also states that after storms the beach is strewed with zoophytes thrown 
up from deep water "Geology of Portland." p. 162). 



ON THE ORIGIN OF THE CHESIL BANK. 19 

of the sea lessening their power : this is accompanied by a gradual 
westward trend of the beach. To the great accumulative power 
and small propelling power, thus exercised, 1 the large dimen- 
sions of the bank and the great wear of the shingle, as it slowly 
travels from Chesilton to Abbotsbury, are probably due. Although 
as the " raised beach " consists of seams of large shingle, and of 
others where the shingle is fine and small, it may be a question 
whether the fine shingle at the Abbotsbury end of the Chesil 
Bank is not in greater part the sorted portion of the old beach 
rather than the larger shingle worn down. 

The westward curve of the bank from Chesilton to Abbotsbury 
seems ^ necessary consequence of the gradual decrease of wave 
power in that direction. When the wind-waves impinge on the 
shore at right angles, as they do westward of Barton in conse- 
quence of the changed direction of the coast, the travelling of the 
shingle ceases. 

The " Fleet " may possibly be regarded merely as a remnant of 
the West Bay at an early period, when that part of it was a shallow 
off-shore, before it was cut off and isolated by the Chesil Bank ; and 
as the shingle has been thrown up on the south end of the bank, 
it has been gradually drifted to the north-west on. a line along 
which the opposing forces of the wind-waves and tidal currents and 
inertia of the mass to be moved were balanced. 2 (Plate 3, Fig. 2.) 

A somewhat analogous case takes place on the coast eastward of 
Portland ; for, while the shingle in the East Bay travels north- 
ward towards Weymouth, Sir John Coode has pointed out that on 
the north side of Weymouth Bay the shingle travels westward from 
Lulworth. The effect of this has been to accumulate a large 
beach between White Xore and Weymouth, which, like the shingle 
in the West Bay, has formed a backwater that passes behind 
Melcombe Begis, and it has also formed, between that town and 
Preston, a bar in front of the Lodmoor marshes, over which the 
sea must formerly have flowed. This westerly movement of the 



1 This is more especially seen in the oolitic pehbles. 

2 Sir Henry De la Beche attributes the low cliffs at the south end of the Fleet 
to the action of springs and the waves ; but the former are comparatively in- 
operative, and the latter are insufficient, as the cliffs occur precisely at the 
narrowest part of the Fleet, where its tiny waves Lave least force ; where the 
Fleet is wider, farther north, there are no cliffs. The cliffs are merely a con- 
tinuation of those in East Buy, with which they seem to have been originally 
connected in an old line passing near the Passage House. The sand at the 
base of the Chesil Bank may be the prolongation of the old strand between the 
East and West Bays. 



20 MINUTES OF PROCEEDINGS. 

shingle is due to the circumstance that Weymouth Bay, while 
open to the eastward, is protected from the west and south- 
west by the Weymouth promontory and the Isle of Portland, and 
consequently the waves raised by the winds from those quarters, 
which are so powerful in the West Bay, have little or no force in 
the East Bay, and are greatly exceeded in power by the waves due 
to the south-easterly winds ; for it has been well established that 
it is not only the actual force of the prevalent winds which has to 
be taken into account, hut also the mass of water they can put in 
motion and the force of the resultant waves. Further eastward, 
where the coast is no longer sheltered by Portland, the westerly 
winds resume their full effect, and the shingle its easterly move- 
ment. 

It follows that there cannot be an uninterrupted travel of the 
shingle up the Channel from west to east, but that there is a 
break at Portland ; and there may be others where similar con- 
ditions are repeated. The presence in the shore shingle of the south 
coast of materials derived from the west of England is no evidence 
by itself of the existing travel of such materials, for the debris of 
the actual coast line is only one element in the formation of the 
shingle beaches. A shingle derived from an " old beach " which 
extended on both sides of the Channel at a former period, together 
with the large mass of angular debris which covered that old 
beach and much land gravel, have been left over parts of the 
Channel bed ; and wherever such old shingle is within reach of 
certain tidal and storm-waves, it will be thrown on, and so add to, 
the present coast-formed shingle. 

This hypothesis is in conformity both with abstract theory and 
practical experience; for the Astronomer Royal, on the occasion of 
the reading of Sir John Coode's Paper, expressed an opinion, based 
on theoretical grounds, that the shingle had travelled from Port- 
land. 1 lie subsequently remarked, "that the travelling of the 
stones would not be from the side where the small stones were 
deposited to the side where the larger stones were deposited; but 
that it must have been in the opposite direction." He supposed 
" that the materials which formed that bank were piled up by the 
sea; that they had been torn up by the violence of the surf from 
the bottom of the sea, and that then, by the continued action of 
the surf, they had been piled up by degrees, and afterwards had 
received some slow motion along the coast: and he was obliged to 
attach to this the additional supposition, that in that part of the 



Vide Minutes of Proceedings Inst. (J.E., vol. xii., p. 554. 



ON THE ORIGIN OF THE CHESIL BANK. 21 

bay under Portland which they were unable to examine, there were 
strata which furnished these coarse blood-stones which had caused 
the difficulty of explanation on this occasion. With regard to the 
mechanical possibility of such a state of circumstances he had no 
doubt." 1 

It was also stated by Sir John that " the prevalent notion amongst 
the fishermen employed on the Bank, and many other practically 
well-informed persons, is, that the shingle travels from south-east to 
north-west ;" and that they say that " the large pebbles are first 
thrown up near Portland, and as they become ground smaller by 
the action of the sea, are gradually washed farther and farther to 
the westward, whilst fresh pebbles are being thrown in at the east 
end, to supply their places." 2 

The one thing wanting in support of Sir George Airy's argu- 
ment was the presence in Portland, or in the adjacent sea, of beds 
which could furnish the particular pebbles characteristic of the 
Chesil Bank. At that time the " raised beach " of Portland Bill 
had not been described. Hence the objections of the Astronomer 
Royal found few supporters. The Author believes that the facts 
here brought forward will show that they were well founded, and 
sums up his views in the following propositions : — 

1st. That the shingle of the Chesil Bank is chiefly derived from 
the materials of the " raised beach," of which a remnant still 
exists in situ on the Bill of Portland, and partly from the harder 
beds of the Portland and Purbeck formations of that island. 

2nd. That the storm-waves, in conjunction with the tidal 
current, drive the shingle of this old beach from the bed of the 
Channel on to the southern end of the Chesil Bank, whence it 
travels by the agency of wind- waves in a north-westerly direction 
towards Bridport Harbour, — at the other side of which the shingle 
travels in the opposite direction, or from west to east. 

3rd. That the growth of the Chesil Bank has been from south- 
east to north-west under the influence of the two above-named 
forces. 

4th. That the shingle of the " raised beach " itself was formed 
of materials which had travelled direct from the coasts of Devon- 
shire and the adjacent parts of Dorset, eastward to Portland. 

5th. That the sea for a time passed between Portland and Wey- 
mouth, and that the Fleet is merely a portion of the old shore-line 
dammed out by the growth of the Chesil Bank. 



Vide Minutes of Proceedings Inst. (J.E., vol. xxiii., p. 226. 
1 Ibid., vol. xii., p. o36. 



22 MINUTES OF PROCEEDINGS. 

6th. That the existing beaches are formed not only of the debris 
of the present coast, but also from shingle derived from old 
beaches, which, together with gravel of a former surface land, is 
now scattered over various parts of the Channel bed, whence it is, 
— under certain conditions of proximity, winds, and tides, — 
thrown up on the present shores. 

The Paper is accompanied by a series of diagrams, from which 
Plate 3 has been compiled. 



i Ml. T. MlCU.AIIJ) PiEADE 



ON THE ORIGIN OP THE CHESIL BANK. 23 

Mr. T. Mellard Reade remarked, through the Secretary, that 
he had inspected the Chesil Bank in November 1873, both at the 
Portland and Abbotsbury ends, and communicated his views to 
the " Geological Magazine." 1 Professor Prestwich's hypothesis 
came upon him by surprise, since he assumed it was a well-ascer- 
tained fact, as stated by Lyell and other observers, that the pebbles 
travelled eastwards and southwards. He was not prepared to 
accept the Author's view without the support of actual experi- 
mental proof. 

The relative mean integral effect of the winds, obtained by 
multiplying the velocity in miles per hour by the number of hours, 
involved, he thought, a mechanical fallacy, if applied to the tra- 
velling of shingle on a sea-beach. The problem was much too 
complicated to be solved in so simple a way. The most important 
element was the wave velocity, and this depended again upon the 
velocity and continuance of the wind. The integral effect — which 
was only the distance travelled by the wind in a given time — might 
preponderate in one direction while the shingle might travel in 
the contrary direction. One strong gale from the westward or 
south-westward might carry the shingle along the beach to the 
eastward, while a continuance of light breezes from the south-east, 
giving a larger integral effect, might not move the beach at all 
westwards. According to the " Sailing Directions of the English 
Channel" the winds, at the entrance of the Channel, " from January 
to May were observed to come from north and north-east, although 
sometimes in January they may be inclined to the south and south- 
westward ; and from January to May, south-westers would 
occasionally occur, yet it would seldom blow long from that 
quarter, but shift round to the westward, and sometimes to the 
north and north-east, but from May to December, westerly and 
south-westerly winds may be said most commonly to prevail." It 
was evident that waves propagated in the entrance of the Channel 
by the prevailing westerly winds would be more effective than 
those across it from the south. It was also known that a south- 
west wind constantly threw a great accumulation of water into 
the English Channel, and augmented the rise of water fully 10 feet 
above its ordinary level. 

It appeared to him perfectly natural that the greatest accumu- 
lation of large pebbles should be found at the eastward end of the 
bank, on the assumption that they travelled from the westward. 
They merely followed the same natural law that determined the 



Vide New Series, Decade II., vo[. i., p. 2S6. 



21 MINUTES OF PKOCEEDINGS. 

size of the bank itself, for where the bank was the highest and 
broadest, the pebbles were the largest ; it also appeared that the 
sub-water beach followed the same law. It must not be forgotten 
that the flood-tide also ran eastward close in shore for nine hours 
out of the twelve, and it was the resultant effect of the two causes 
that must be taken into account ; for though the tide alone might 
be powerless to move the pebbles, while they were lifted in the 
water by the wind-wave, the general current would be certain 
to influence the direction in which they were thrown down 
again. 

No doubt the Author was right in assuming that a large 
portion of the shingle was redistributed beach or drift of a former 
period ; but leaving out of the question the possible former agency 
of ice, if a stone 4 inches in diameter were ground down to the size 
of a bean in travelling 16 miles from Portland to Burton Cliff, what 
size must the stones have been originally when torn from their 
parent Devonshire rocks ? The form of the stones at the Portland 
end, flattened ovoids, and at the Abbotsbury end sub-spherical, was 
against the theory that they travelled westwards, as the attri- 
tion in such travel would be more likely to exaggerate their flat- 
ness than otherwise. Taking all things into consideration, he 
could but adhere to the opinion that the general movement of the 
shingle was eastwards, and that the largest stones were thrown 
up most abundantly at the point where the height and direction of 
the bank showed that the wind-waves from the west were the 
strongest. There were stones sprinkled among the shingle at 
Abbotsbury almost as large as those at Portland, but they became 
more plentiful to the eastward. It was not, as Sir John Coode 
supposed, that the large stones were the more easily moved, for 
the reverse could be readily proved, but the lateral movement 
would be the more constant, as they would remain in the grasp of 
the waves until they arrived at the point of intensest action, and, 
being there thrown iq->, increase the bulk of the bank, a great 
quantity, but not all, of the smaller shingle getting thrown out 
earlier. The large stones, in fact, travelled up a lesser gradient, 
and consequently to a greater distance. The size of the stones again 
diminished as the bank joined on to the Isle of Portland. Were 
the movement of shingle westward, he should expect the bank to 
begin at Blacknore Point instead of at Chesilton. To accept the 
Author's hypothesis involved the great difficulty of believing that, 
while undestroyed by travel from Devonshire and Cornwall, the 
pebbles were, in travelling 16 miles in the opposite direction, so 
ground down as to disappear in the form of fine gravel or sand. 



ON THE ORIGIN OF THE CHESIL BANK. 25 

All experience proved that pebbles accumulated at the leeward end 
of a bank, and at that point, instead of disappearing, the bank 
tended to increase in magnitude. 

Mr. W. Topley, of the Geological Survey of England, remarked, 
through the Secretary, that the Paper reopened the discussion of a 
question which had been considered as settled for some years past. 
Since the publication of the Papers by Mr. Redman and Sir John 
Coode in the Minutes of Proceedings of the Institution, there had 
been but little disposition on the part of either engineers or geo- 
logists to dispute the correctness of the results then generally 
arrived at:— (1.) That shingle travelled in the direction of the 
prevailing wind ; (2.) That the larger pebbles travelled faster and 
farther than the ' smaller pebbles. The Author admitted the cor- 
rectness of the first, but disputed the second, supported by the 
high authority of the Astronomer Royal. The question was one 
of great importance, because it applied to all shingle beaches, and 
'not to the Chesil Bank alone. Apart from the existence of the 
" Fleet," the Chesil Bank was remarkable for its great length, un- 
broken by any artificial groynes, and for the regularity with which 
its pebbles were sorted. For these reasons it was difficult to prove 
the relative rate of travel of various sized pebbles. But in beaches 
farther east, along the coast of Sussex and Kent, the point could be 
easily tested. Where effective groynes existed the shingle might 
be regarded as several detached beaches, each of which could he 
studied separately. In each separate area it was found that the 
largest pebbles had been carried towards the east, or to leeward, 
and to the summit of the beach. But this only occurred after the 
prevalence of westerly or south-westerly winds. Should the wind 
change to the east or south-east, and so blow for some days, 
the distribution of the shingle in each compartment was com- 
pletely reversed. The larger pebbles travelled back towards the 
west, and accumulated against the higher part of the westward 
groyne. Of this fact, which was probably a matter of common 
knowledge, he could speak from personal observation at Hastings. 
"What was true of small compartments of beach was true of long 
stretches of shingle, except that the abnormal winds never lasted 
long enough to reverse the arrangement of the pebbles in the latter. 
It was admitted that the shingle of the raised beach of Portland 
and that of the Chesil Bank originally came from the coast of 
Devon and Cornwall ; notwithstanding this long journey, pebbles 
of large size arrived at Portland. But on the assumed return 
journey from Portland to Abbotsbury, a distance of only 11 miles, 
it was supposed that the pebbles had been enormously worn down. 



26 MINUTES OF PROCEEDINGS. 

For even if the main result of wave action was to sort the 
shingle of the bank, carrying the smaller pebbles rapidly west- 
wards, yet it was not denied that the shingle, as a whole, did 
travel, consequently the larger pebbles must become worn down. 
To take again an example from the south-eastern coast : — There 
could be no doubt that the shingle of Dungeness had travelled past 
Langley Point, a distance of 30 miles, yet there was no notable 
difference in the size of the pebbles. The shingle of this coast, as 
a whole, was remarkably uniform in character, differing only at 
various points between the groynes, where the sorting action of the 
waves came prominently into play. Having regard to the north- 
westerly range of the Chesil Bank, and the supposed direction of 
the prevailing winds, it was at least open to question whether the 
direction of travel of the shingle should not be from south- cast to 
north-west, as the Author affirmed it to be. But it was of great 
importance to obtain better information as to the direction of the 
winds than was contained in the records quoted in the Taper ; for 
these records were from old sources, and were continued for only 
a short time. It was not necessarily the mean annual direction 
of the wind which controlled the movement of shingle. The 
relative velocity of the winds, and especially the power and dura- 
tion of the waves raised by the respective winds, must be taken 
into account. Winds which blew directly on shore should pro- 
bably be omitted from consideration ; for these had no influence 
over the travel of the shingle, whatever their effect might bd 
in piling it up. Yet the omission or admission of these winds 
might make a great difference in the mean result obtained. 
One other consideration suggested itself in comparing the I ShefiiJ 
Bank with other beaches. The travel of shingle to leeward was 
checked, sometimes arrested, by a tidal inlet. On the banks of the 
inlet, but especially on its lee side, there was frequently an accu- 
mulation of blown sand. Without now discussing the cause of 
this, it was sufficient to notice that at the south-east end of the 
Chesil Bank there was blown sand. If the known facts regarding 
other beaches were to help in solving the problem presented by the 
Chesil Bank, the conclusion would be that the shingle travelled 
from west to east, and that the blown sand occurred just beyond 
the point where the travel of shingle ceased, or was largely 
checked. 

The Eev. Osmond Fisheb said he had recently written upon the 
subject in the "Geological Magazine." 1 His views were very 



Vide New Series, Decade II., vol. i., pp. 11)0 and 28;"). 



ON THE ORIGIN OP THE CHESIL BANK. 27 

similar to those of Professor Prestwich, only that gentleman had 
taken into account the old raised heach. Any one who observed 
the accumulation of beaches along the south coast could not fail to 
see that it had been the work of a long time. The pebbles had 
not been derived from the present coast-line in a short period ; 
and the inquirer was therefore naturally thrown back upon past 
geological ages. Professor Prestwich had pointed to the age of the 
raised beach as that in which the pebbles were washed out of 
their matrix (whether gravel or triassic shingle beds or greensand 
chert beds) and since washed forward to the Chesil Bank. He 
thought it was hardly necessary to confine the accumulation chiefly 
to a particular period. It must have been a long, progressive 
work. Ever since the time of the raised beach the coastdine had 
been eroded, and fresh accumulations of pebbles had been added. 
He had been constantly impressed with the fact that the 
present contour of the land was very ancient. There was no 
gradual descent of the surface towards the sea margin ; but there 
were ranges of hills, not diminishing in altitude as they reached 
[the coast, as they ought to do if the coast-line and the present 
surface contour had been equally recent. The hills must at one 
time have gradually sloped down to the edge of the water, and it 
must have taken a long time for the water to have eaten them 
back to the point which the coastdine at present occupied. There 
were gravel beds about Weymouth which consisted principally of 
greensand chert. They were not water-deposited beds, but more, 
like denudation gravels that appeared to have come from a former 
continuation of the greensand hills southward, and to have been 
carried on thence by surface action. He differed from Professor 
Prestwich as to the formation of the Fleet. There were no cliffs ; 
the contour of the surface came gradually down to the water's 
edge, and he regarded the Fleet as a portion of an old submerged 
valley similar to that which now formed the Weymouth Backwater, 
or those which constituted the Southampton Water and Poole 
Harbour. The sea had raised a beach before itself, which had 
been gradually driven forward, as the old land was being destroyed, 
until it intruded upon the submerged valley. If Portland were 
removed, the beach would still advance in the same direction, the 
land being cut away in front of it, until it attained a position 
across the middle of Weymouth Backwater, in which case the 
eastern side of Weymouth Backwater would form a backwater 
exactly similar to that of the Fleet. That was his theory as to 
the formation of the Fleet. He did not believe that its coast had 
ever been exposed to the action of the waves of the West Bay, 



28 MINUTES OF PROCEEDINGS. 

otherwise the coast-line would have been without indentations, as 
at present, and with steep cliffs. 

Mr. John Dunning said he lived about a quarter of each year at 
Sidmouth, where, being at the innermost point of the bay, the 
action of the moving shingle could be most carefully watched. 
He had spent hours in watching it when the wind was blowing 
strongly from S.S.W. and S.W., and had observed that it moved 
very rapidly. He was told by the inhabitants that twenty years 
ago the shingle bank in front of the west end of the esplanade 
wall was about 20 feet deep, extending from the face of the wall 
to high-water mark ; whereas now the wall was completely under- 
mined at that end by the sea and was in a dangerous state. He 
had noticed that the shingle seemed to travel round Otterton Point 
and strike immediately to the west of the Chit Ledge, a mass of 
projecting rock. Inside the bay, on the west of this mass of rock, 
there was but little shingle ; at that point the shingle passed over 
the rocks which were half-tide high, and travelled away eastward. 
It was the general impression of those who had watched it, that 
there was a decided movement of the shingle from the west towards 
the east, so much so as to cause considerable anxiety. AYhen an 
E. wind set in, the shingle was brought back again to some extent, 
and after a heavy gale from S.E. there was a considerable quantity 
piled up rapidly at the west end of the esplanade, but as soon as 
the wind and waves turned, it disappeared either slowly or rapidly 
according to the force of the waves. The prevalent storms being 
S.W., there had been for many years a decided decrease in the 
quantity of shingle at that point. Stones had been marked, 
and had been found to travel along the coast. He therefore 
agreed with the opinion that the shingle travelled from vest to 
east. The bay in question, from Start Point to Portland Bill, was 
a large one ; the waves came in with terrific force, and would 
probably sweep round near Bridport, so that a circular motion 
would be given to the action of the tide, which would easily account 
for the shingle being assorted b}' the waves in the manner so 
peculiar in the Chesil Bank. Even on Budleigh Salterton beach 
the sand was at the bottom, and the sea evidently moved foil 
ward the stones of greater area until at length the largest 
were found at the top. The same process was observable on 
almost all such beaches. He had recently seen a stone, the size 
of his doubled fist, which had been thrown by the force of the 
waves over the wall on to the esplanade at Sidmouth, a dis- 
tance of 30 feet, while no sand to any serious amount was cast 
up there. This appeared to prove that the large stones, having 



ON THE ORIGIN OF THE CHESIL BANK. 29 

a greater area exposed to the action of the waves, were sent the 
farthest. 

Captain Burstal said the subject was one of great interest to 
him, having for many years been employed on the coast survey. 
He had not had much opportunity of watching the action of the 
tide between Portland and Torbay, but it was a general rule on 
the south and the east coasts that the shingle travelled with the 
prevailing waves, and was very little acted upon by the current. 
He had been chiefly employed between Bognor and the Forelands, 
and there invariably, except with E. winds, the shingle travelled 
from west to east. At Shoreham, Newhaven, Folkestone, and 
Dover shingle bars had been prevented from accumulating by a 
judicious arrangement of groynes. The groynes at Hastings and 
Brighton were heaped up on the west side, while on the east there 
was a descent of from 5 to 6 feet. Large quantities of shingle 
were sometimes found at sea. At a distance of 5 or 6 miles to the 
south of Hastings he had found, in making the survey on which 
he was employed, large shingle banks, the shingle being as clean 
as that on the beaches. One of these banks was 4 to 5 miles in 
length, running E.S.E. and W.S.W. Between that point and 
Hastings the ground was sand. He had also found a large quan- 
tity of shingle on the Harwich coast, about 5 miles north of the 
Kentish Knock. On the Essex and Suffolk coast a supply of shingle 
was obtained from the east, whence the heaviest seas came, namely, 
from Orfordness along the coast to Landguard Point, at Harwich. 

Admiral Strait said he had not been employed upon the south 
coast, but he had given some attention to the movements of 
coast beaches, and he agreed with Captain Burstal that the 
shingle beach movement was mainly due to wave action, the tidal 
influence being very small. The wave action or movement gene- 
rally resulted from the line of direction and force of the prevailing 
wind. With regard to the origin and character of the shingle at 
the Chesil beach near Portland, he thought that the existence of 
the old raised beach at the Bill was in reality the key of the 
whole question, taken in connection with other similar raised 
beaches near Torbay, and with the identity of its pebbles with 
them and with the pebbles forming the present beach at the back 
of Portland. The Author had a right, therefore, -to conclude that 
there was formerly an intermediate connection between these old 
beaches on a line of old coast such as he had described, although 
probably not in the exact position, but somewhere in the line indi- 
cated on the map. He had clearly demonstrated, too, that the 
main movement of the western portion of the Chesil beach was 



30 MINUTES OF PROCEEDINGS. 

from west to east, and of the eastern portion slightly from east to 
west. Sir William Eeid some years ago came, however, to the 
conclusion that the movement was entirely from west to east 
along the whole length of this coast, because a cargo of coal, from 
a vessel wrecked near Lyme Eegis, was scattered considerably to 
the eastward into the bight of the bay. That fact seemed to 
indicate a constant eastern movement ; and it had been con- 
cluded, by Sir William and others, that it was continued all 
the wuv to Portland, but he did not now see how that could 
possibly be the case. For it would be obvious from an inspection 
of the chart, that the line of direction of the greatest wave action 
at the head of the bay was in the line of greatest fetch of the 
sea, viz., from the S.W. or S.S.W. : from the mouth of the channel, 
and therefore the stroke was almost parallel to the beach there ; 
so that there could never be very much movement from west to 
east at that point. With regard to the largest shingle being all 
found in the angle or bight of the bay. it was effected by the 
dominating wave-stroke being from the south and south-westward. 
Therefore that corner was a sort of pocket that had received and 
retained it all, as a result of this wave-stroke and of the waste of 
the old raised beach near it. 

Mr. H. B. Maqkeson said he had carefully watched the motion 
of shingle, and he could tell a tale of even greater denudation than 
that which had been described. There had been at Hythe a loss 
of 130 feet or 150 feet of foreshore within the present century, and 
it was still going on, largely owing to the accumulation at Dungel 
ness Point which intercepted the shingle. He agreed with the 
view already expressed, that the movement of shingle was due 
entirely to the action of the waves ; this depended upon the pre- 
vailing winds, which were westerly. He wished to direct atten- 
tion to a most exhaustive paper by a gentleman whose name he 
had not heard mentioned in the discussion, Mr. Henry Robinsdj 
Palmer, Yice-President Inst. C.E.. in the "Philosophical Transac- 
tions." 1 That gentleman, he believed, was one of the first who had 
written upon the subject. 

Mr. Bramwell objected to the statement that the larger sr.mes 
would go farther than the others because they had more surface. 
Taking a piece of cork a foot cube, one could not blow it along, 1 >ut 
a piece of gold leaf could be blown along ; yet gold was of much 
greater specific gravity than cork. The reason for this was that. 
with small articles, the areas decreasing only as the scpuares, while 



1 v;<l< -Phil. Tnras.," L884, p. 5ffi 



ON THE ORIGIN OF THE CHESIL BANK. 31 

the bulk decreased as the cubes, the areas were much greater in 
relation to the bulk, and therefore small bodies would obey a force 
which larger bodies would not. He would cite two instances to 
show that the statement made was wrong. In a stream coming 
from the foot of a glacier, running in a small channel with great 
rapidity, stones were found larger than a man's head ; but a few 
yards farther on they were diminished to the size of a man's fist ; 
yard after yard they became smaller and smaller as the stream 
became less rapid, until at length there was but the milky- white 
of a glacier stream, which required the quiescence of a great lake 
to deposit it, since the smallest current would carry it along. In 
plate-glass manufacture use was made of this property for the 
purpose of bringing about a separation which could not be effected 
by mechanical means. In grinding emery for that manufacture, 
it was necessary to separate it into a variety of qualities, to be 
used successively for polishing glass. If among the emery of finer 
quality there was a single particle of the coarser, the whole work 
would be useless. It would inflict a deep scratch, and the work 
would have to be gone over again to get the scratch out ; so that it 
was absolutely necessary to have an accurate division of the emery. 
This was accomplished by a succession of vessels, say a dozen, 
through which a stream of water flowed, in at the top of one, 
down a central pipe, overflowing an outer case, into the central 
pipe of the second, overflowing the outer case of the second, and so 
on ; each vessel being larger than the previous one, and the quantity 
of water being the same, the current was diminished in each vessel, 
so that the emery was separated into different qualities, the smaller 
emery going with the weaker current. Those two instances showed 
that it was the smaller particle that went with the feebler cur- 
rent. It was wrong therefore to say that the reason why the 
largest stones went the farthest was because they had a greater 
surface exposed. They had a less surface exposed, in reference to 
their cubic contents. The reason was that they had greater weight 
and greater momentum. A wave going along with a force suffi- 
cient to move heavy bodies, and therefore to move lighter ones, 
met with the obstruction of the beach upon which it was breaking : 
smaller bodies not having momentum enough, were arrested, and 
heavy bodies, having more momentum, went on to higher points, 
which they did by virtue of their greater cubic contents, and not 
by virtue of the supposed larger surface. 

Admiral Spratt said that on one occasion, on the coast of Egypt, 
he put overboard five bags of clinkers, weighing from 3 lbs., 4 lbs., 
and 5 lbs. to a few ounces ; and on visiting the spot a fortnight 



32 MINUTES OF PROCEEDINGS. 

afterwards to examine the effect of wave action, he found at 450 
yards to leeward the largest pieces of clinker nearest the point of 
starting, one weighing 3\ lbs. and the others 2 lbs. ; at 700 yards 
and 800 yards they weighed less than 1 lb., and at 1,500 yards or 
1,600 yards from ^ to £ oz. only. Thus the heaviest and largest 
pieces certainly did not travel the farthest, but the contrary. 

Mr. Cowper said he agreed with Mr. Bramwell, who might, 
however, have added, that the larger pebbles were landed and 
anchored, so to speak, on the beach when thrown up, and the 
smaller ones and sand washed back by the return of the wave, as 
might be seen on any beach. 

The Astronomer Koyal said he wished to express his satisfaction 
that the Paper contained a recognition of the principle he was so 
anxious to urge upon the Institution at a former Meeting, that the 
progression in smallness of the pebbles pointed to the direction 
from which the current or fluctuation must have transported them, 
and that they must have been transported from the end of the bank 
where they were large, towards the end where they were small. 
It also afforded him great satisfaction to find that there existed 
materials in one part of the Island of Portland, namely, exactly at* 
the point of the Bill, which accounted in some measure for the 
nature and the magnitude of pebbles which might have been, at a 
former time, rolled from the north-west direction towards Portland. 
Yet, looking at the maps, and observing the small extent of the 
raised beach to which reference had been made, in comparison with 
the enormous extent of the Chesil Bank, he could hardly imagine 
that there had been materials enough at that place to account for 
the formation of the whole bank. He was therefore in some clif- 
culty on that point, because it was hard to say how much material 
there might have been formerly, which had now disappeared in 
the formation of the bank ; but, presuming that the part removed 
was less than that which remained at the Bill, he thought there 
were not materials enough to form the bank. He observed that 
in the map (Plate 3) the line conjecturally given as that of the 
ancient beach was much in advance of the present beach. He 
apprehended that the existence of such a beach in front of an 
existing beach in a bay was a thing that did not commonly happen. 
Seasoning from small ba} T s to large ones, he could say it certainly 
did not happen. The tendencj^ in small bays, of which there were 
instances along the limestone coast to the west of Swansea, was for 
the points of the cliff terminating the bay to break down, and to 
be washed on to the beach in the middle of the bay. This was 
the tendency in all cases where there was a slope. It was so 



ON THE ORIGIN OF THE CHESIL BANK. 33 

even in shallow water, and it made the water assume that pecu- 
liarly disturbed character in which the rise was more rapid than 
the fall. If the water was moie shallow, the slope made it 
break in surf, in which case the difference to which he alluded was 
still more remarkable. The rise of water was more rapid and 
violent than the fall ; it carried up materials which the fall could 
not bring down, and invariably the beach was heaped up in the 
bay. It might be difficult to say how far he was entitled to com- 
pare a small bay with a large one like that extending from Start 
Point to the Bill of Portland ; nevertheless, he believed that the 
same principle held in great measure, and that the action of the 
sea, so far as it had affected the beach at all, was to add to it 
instead of taking away from it, and that the beach therefore at 
distant times was more retired than now, instead of being more 
advanced. He was sorry to believe this, because he should have 
been glad to think, looking at the form of the beach in distant 
times, and to the current which might be supposed to prevail from 
the same quarter as the prevalent winds, that the blood-stones and 
other things found in the Chesil Bank had been carried along in 
that direction, but he could hardly conceive it to be so. The only 
place from which he could imagine the stones to have been brought 
was some nearer source. When speaking on the subject on a 
previous occasion, he found himself in great difficulty of explana- 
tion, and said that he could only imagine the stones to have been 
pulled out from the bottom of the sea ; l and he was partly driven 
to the same view still. In forming an opinion on a question of 
that kind, one naturally looked at other subjects of a kindred 
character. He had previously directed the attention of the Insti- 
tution to a district with which he believed the Author of the 
Paper was not unacquainted, Landguard Common, near Harwich, 
where there was a flat tract of shingle pebbles 1 square mile in 
extent; 2 and, looking at the intersection of the ground by the 
rivers, and at the cliffs on both sides for a considerable dis- 
tance, there was nothing in the neighbourhood of the shore, or at 
the boundary between land and water, which could account for the 
formation of that great mass of pebbles. Yet it was still growing, 
and was a great trouble to the nautical authorities of the country. 
This was at one time warmly taken up in the Tidal Harbour 
Commission by the late Captain Washington, who supposed that 
the run of the water out of the Orwell and of the Stour, and out 
of Harwich Harbour, had been greatly influenced by the removal 

1 Vide Minutes of Proceedings Inst. C.E., vol. xxiii., p. 228. 
- Ibid., vol. xxiii., p. 238. 
[1874-75. N.s.] IX 



34 MINUTES OF PROCEEDINGS. 

of stone for Roman cement; and a useful channel was actually 
stopped up in Harwich Harbour in order to throw the current in 
a different direction. It had not the slightest effect, but produced 
great inconvenience, and the formation of the shingle on the outside 
of Landguard Common was still going on. The position of the 
lighthouses had consequently been twice changed since he had 
known them. In that instance he could not resist the conviction 
that the pebbles had come out of the sea. The cliffs along the 
coast were partly crag and partly London Clay. Below the clay 
there Avas, generally speaking, the stratum of pebbles which 
absurdly went by the name of ' plastic clay formation.' He thought 
that in all probability these pebbles extended as a bed under the 
clay cliffs into the sea. that there was an immense quantity of the 
pebbles outside Landguard Common, and that the sea was con- 
stantly heaving them up. He wished very much that he could 
induce some competent persons to examine the deposits 2 or 8 miles 
out. Perhaps the same remarks applied to Denge Common, the 
great plain of shingle which terminated in Dungeness. Enter- 
taining the conviction he had expressed with regard to those 
pebbles, it influenced him in a great measure in judging of what 
had passed in the locality in question, and he unwillingly adhered 
to the view he had previously expressed, that a great part of the 
Chesil Bank had actually been pulled up out of the bottom of the 
sea by the enormous agitation of the water sometimes taking place 
there, which no one could conceive without having actually wit- 
nessed it. In the examination of the coasts several places might 
prove very interesting. One of these was Sidmouth, where there 
seemed to have been a sort of convention between the sea and the 
little river which flowed into it ; the sea allowed the coast road 
to be carried across the river without a bridge, and the river sub- 
mitted to the indignity of percolating through the pebbles. That 
was the only place where he had seen anything of the kind. It 
would be well worth an examination to ascertain conjecturallj T the 
cause of the large collection of pebbles at that spot, and what 
was their character and general nature which allowed such a 
passage of water through them. He had nothing further to 
add, except to acknowledge that a distinctly new and valuable 
element had been introduced into the subject by the discovery 
and recognition of the beach at the Bill of Portland. The 
upper raised beach, he imagined, could never, at least dining 
the present shape of the country, have had any particular eflect, 
although it might have influenced its former shape before the 
country was so much raised as to give it its present appearance. 



ON THE ORIGIN OF THE CHESIL BANK. 35 

Mr. J. Thorxhill Harrison" said that some years ago he had 
occasion to examine the West Bay for the purpose of preparing a 
Paper for the Institution,' when he obtained a considerable amount 
of information. He would, in the first place, explain what that 
information consisted of, then review the several theories advanced 
as to the origin of the Chesil Bank, and, finally, explain what 
appeared to him to be a proper solution of the question. The 
information he had obtained was derived from fishermen em- 
ployed in the West Bay ; and he had compiled a map showing 
the result of his inquiries. The first submerged rock to which he 
would direct attention was that known as " Paignton Scrag," 
lying about 20 miles from the Start, outside a straight line from 
the Start to the Bill of Portland; this rock was 8 or 10 miles long, 
and about 1^ mile in breadth, and stood about 18 feet above the 
general bottom of the bay, in 30 fathoms of water. At each end, 
for a considerable distance, there were numerous sea urchins, 
locally called ' scruff.' Another well-known rock, called the 
" Exeter," lying 10 miles S.E. of Teignmouth, about 1^ mile in 
length, and 1 mile in width, rose between 60 and 70 feet above 
the bed of the bay, in 26 fathoms. The fishermen stated that 
rocks extended inland 7 or 8 miles continuously from the " Exeter," 
and that towards the north and north- east, even as far as Bridport, 
at distances of 1 mile or lj mile apart, the whole of the bottom of 
the bay was studded with detached rocks. In the direction of 
Portland there were several beds of rock jutting out in different 
directions, and others just beyond the Bill of Portland. Between 
the rocks all over the bay there was excellent fishing. Indeed, 
inside the Start there was one of the largest fishing-grounds in 
England. The bottom was muddy sand, there being scarcely any 
clean sand over the bay. The next point to which he desired to 
allude was, the position of the gravel upon the beaches and in 
the bed of the bay. When he was engaged on the South Devon 
railway, Mr. Le Gallais visited, for Mr. Brunei, every bay round 
the coast, took cross sections, and in some cases made surveys of 
them, and gave a description of the pebbles found in each of the 
bays and in the cliffs adjoining. When Mr. Le Gallais came to 
Budleigh Salterton Bay he found an entirely new description of 
gravel upon the beach, differing from anything between the Start 
and that point. Some of the pebbles weighed from 10 lbs. to 1 2 lbs., 
and were similar to those found upon the Chesil Bank. Coming to 
Otterton Bay, he again noticed a distinct character of shingle ; in 



Vide Minutes of Proceedings Inst. C.E., vol. vii., p. 327. 

D 2 



30 MINUTES OF PROCEEDINGS. 

fact, each bay appeared to have its own distinctive shingle similar 
to the gravel and flints found in the cliffs adjoining. The only flint 
common to them all was the yellow flint derived from the raised 
beach capping the cliffs almost throughout the entire length. The 
point to which he desired to draw attention was, that the hay was 
being encroached upon, and had been encroached upon, for many 
centuries past; that in all probability the land at one time ex- 
tended far out into the West Bay — perhaps as far as the Exeter, 
in which case the tide would pass unimpeded up the now nearly 
closed estuaries of the Teign and the Exe, and the Eiver Axe, 
and rise to a very considerable height. There was abundant 
evidence in several of the present estuaries to show that such 
had been the case. The' tide, for example, was well known to 
have flowed 20 miles above Exeter ; mooring chains and many 
remains connected with shipping had been found in situations 
where now there was no tidal water at all. In the Eiver Axe 
a large vessel was discovered under the bed of the river, which 
could not have got there by the present channel. The ancient 
Eoman station " Moridunum " was believed to have been upon 
the Eiver Axe, and that view was strengthened by the many 
Eoman remains found in the neighbourhood. The account given 
of the distance of Moridunum from Exeter and Dorchester would 
place it a' long way from the present shore. Again, both the 
Axe and the Teign were skirted by bold cliffs, which could only 
have been formed by exposure to the sea in an open estuary. He 
therefore concluded that a great part of the West Bay had been 
encroached upon by the sea, and that, although the general bed of 
it had been excavated to a depth of 10 fathoms to o0 fathoms, a 
large amount of rocky material still remained. No wind-waves 
acting upon a beach would ever have excavated the bed of the bay 
to its present depth, and some other forces must therefore have 
been in operation. Among those forces, he believed, were the tidal 
action, 1 which was very considerable in the bay, and the ground- 
swells, which came into it with enormous violence. Those forces 
were still in active operation ; and in all probability there were 
in the submarine rocks to which he had alluded sufficient ma- 



1 Information was desirable as to the effect, on the bed of the sea, of the tidal 
wave, 'when the momentum is changed from a large volume of water, of great 

depth, moving with small velocity to a small volume of shallow water moving 
with great velocity, and when the rise of tide is increased within a short distance 
from 3 or 4 feet to 18 or 20 feet, or much greater heights. The eroding < tlV-'t 
on obstructions is then probably very great, and the tidal wave becomes a gigantic 
ground-swell. 



ON THE ORIGIN OF THE CHESIL BANK. 37 

terials to supply the shingle of the Chesil Bank. With regard 
to the submarine shingle, gravel was found to a distance of 
20 miles from the Start Point towards the Bill of Portland. In 
the description given in the "Sailing Directions" accompanying 
Norie's Map, it was stated that, to the westward of Portland, there 
was an anchorage, and that that anchorage was shingle. " The 
Race " was another mass of shingle ; he had been accustomed to 
regard it as simply the rapid current which was known to pass 
round the Bill of Portland ; but that was not what was meant by 
" the Pace." The description in the " Sailing Directions " stated, 
" The race is a great rippling of the water, caused by the uneven- 
ness of the ground over which it flows. In the Pace you will 
shoal from 18 to 7 fathomfe, and quickly deepen again to 10 and 15 
fathoms, and you will continue to do .so until you are through it. 
At spring-tides, and when the sea is high, it breaks exceedingly, 
making it very dangerous for small laden merchant ships. The 
distance of the Race from the Bill of Poi tland varies ; when the 
wind is from the north, the distance is about If mile ; when it is 
from the west, it is driven to within j of a mile from the Bill." 
He considered that "the Race" was neither more nor less than the 
bar of the bay. From the Race towards the middle of the English 
Channel the bottom was covered with gravel for a distance of 
20 miles. The tidal current was known to set in from the Start, 
past Berry Head, across towards Budleigh Salterton, thence along 
the coast towards Lyme Pegis, turning out again to the Bill. By 
that course it left two considerable bays where there was hardly 
any current, one on the western, and another on the eastern side of 
the West Bay. After a heavy flood of rain, when the water of 
the Tei<;n came down discoloured, he had seen the discoloured 
water flow out, as the tide ebbed, for a considerable distance to sea, 
in the shape of a fan, and when the tide flowed again the whole of 
it re-entered the Teign, so that there could hardly be any along- 
shore current. The current, however, passing the Exeter, along 
the coast and back again to the Bill, was of considerable force. 
So important was it, that when the fishermen were beating to 
windward they never thought of hugging the shore, but got out 
into the current. With regard to the source from which the shingle 
of the Chesil Bank had been derived, the observations of Mr. 
Le Gallais had convinced him that the shingle did not travel from 
Budleigh Salterton along the bays to the Chesil Bank. The 
shingle was not to be found there. He did not think that there 
was any subuierged beach in the form mentioned by Professor 
Prestwich : but he believed that some of the shinjrle from the 



38 MINUTES OF PROCEEDINGS. 

Bill of Portland might be carried back. The Astronomer Royal's 
view, that the materials which formed the bank were piled up by 
the sea, after having been torn up by the violence of the surf from 
the bottom, coincided very nearly with bis own. An objection 
had been raised that there were no forces in operation in the bay 
that could carry the materials from the rocks to the Chesil Bank. 
In the discussion that took place on the reading of Sir John 
Coode's Paper on the Chesil Hank in May 1853, the remarks made 
by many gentlemen as to the power of the sea to carry materials 
along were, to his mind, quite conclusive. 1 The following extract 
from a Paper on the Bed of the German Ocean by Mr. Stevenson, 
who had had great experience, was much to the point. ''Some 
drift stones of large dimensions measuring upwards of 30 cubic feet, 
or more than 2 tons weight, have, during storms, been thrown upon 
the [Bell] Eock from deep water. These large boulder-stones are so 
familiar to the lighthouse keepers at this station, as to be, by them, 
termed ' travellers.' " 2 Besides, there was the evidence that the 
hay was excavated to a depth of 10 fathoms, or 60 feet, within 
a mile of the beach, near Lj'ine and Bridport, and the encroach- 
ment was still going on. Tins was a gradient of 1 in 90, quite 
sufficient for the undertow of the ground-swell to draw out 
the stones falling from the cliffs ; and any boulders that might, 
by the incessant action of the tidal current upon the rocks, be 
separated from them, became powerful engines, when knocked 
about, in disintegrating the remainder of the rocks. Sir John 
Coode said that at the western end of the Chesil Beach there 
were large round pebbles of considerable weight below water 
mark, and that they diminished in size very decidedly at the 
eastern end of the beach. Now, what would be the effect on 
stones detached from the rocks, and carried along the coast in 
dee] i water, knocked about here and there, and having their 
edges rubbed off in all directions? They would be formed into 
round pebbles, very different from the pebbles found upon the 
Chesil Peach, which were flattened by stones rolling over them. 
The view he took was. that from the part of the coast men- 
tioned by Sir John Coode, and from the submarine rocks to 
which he had referred, the materials were brought along the coast 
and deposited in the shingle bed. which formed an anchorage 
for vessels westward of Portland in the Pace, and beyond 
for 20 miles towards the middle of the Channel, and that the 



Vidt Minutes of Proceedings Inst. C.E., vol. xii., j>p. 551, 552. 
Ibid., vol. vii., p. :;:;;:. 



ON THE ORIGIN OF THE CHESIL BANK. 39 

shingle forming the anchorage was in a right position to be acted 
upon by the violent south-west winds, which drove it on to the 
Chesil Beach. It would be observed by the map, that the 30-fathom 
contour line approached close and parallel to the east end of the 
Chesil Beach ; the effect of that would be to allow the waves to 
fall with their full force during a storm on to the east end of the 
Chesil Beach : and their force would be diminished towards the 
west end of the beach. The result was that the beach, consisting of 
large shingle, was thrown up to a great height at the Portland end, 
and to a much less height towards the Abbotsbury end, where it was 
composed of much smaller shingle. One point mentioned by Sir 
John Coode, with regard to the character of the shingle upon the 
Chesil Beach, appeared to him to be very important ; not only was 
the beach at the east end thrown to the highest level, and the 
shingle the largest, but the largest pebbles were found about the 
level of high-water mark ; and the smallest were thrown on to 
the top of the beach, the shingle from high-water mark downwards 
gradually diminishing. He considered that the direction of the beach 
was determined by the prevailing wind, to which it ranged very 
nearly at right angles. A most interesting question, raised by the 
Bev. 0. Fisher, was how it happened that the beach lay in the direc- 
tion apparently of an old estuary, and that the land on the opposite 
side had never been encroached upon. His impression was that 
Portland extended westward to a considerable distance, and the 
several rivers that now debouched into the bay came along that 
channel, and that as the encroachment was made through the land 
on the western side of the estuary, the beach constantly followed 
up and closed between the mainland and what would otherwise be 
an island. 

Mr. Whitakkr remarked that the Author, following the opinion" 
of the Astronomer Boyal, thought that the increase in the size of 
the pebbles eastward was fatal to the theory of easterly progression. 
Was it, however, an ascertained fact that in all cases the smallest 
pebbles were carried farthest along a beach, as they were in 
running water ? He had noticed that where groynes stopped the 
progress of shingle— as, for instance, in the neighbourhood of 
Felixstow — the large stones were often carried farthest, and 
deposited in the highest part of the beach. The Author also 
remarked that, with the easterly movement supposed by Sir John 
Coode, there would not be the increase in the size of the bank 
towards Bortland : but it appeared to him that this should be just 
where there was an increase in the impediment to progress, cr 
where it was at the present time, at the south-eastern end of the 



40 MINUTES OF PROCEEDINGS. 

bank, where the pebbles, if they had such a course, were prevented 
from going any farther by the projection of the great natural 
groyne of Portland. With regard to the material of which the 
bank was formed, he agreed with the Author that a great dial of 
it might have been derived from a further extension of beach, like 
that which remained at Portland Bill : and it should be remem- 
bered that the beach must have extended more or less across from 
Portland towards Torbay. The Author allowed an easterly flow 
of shingle as far as Burton Bradstock ; beyond that he inferred 
that the current was in an opposite direction, or about north-west. 
If that were the case, two opposing currents of shingle met at one 
point ; and surely at that point there ought to be a very large 
beaching up of the shingle. But that was just the point where 
there was the least, the greatest quantity of shingle being at Port- 
land. The Author remarked that a beach of shingle was thrown 
up a little north of Weymouth, caused by two opposing currents ; 
but if that was the case on one side of Weymouth, it ought to be 
the case on the other, under like conditions. As the old raised 
beach was known to have extended much farther west than at 
present, the fact of the Chesil Bank having been gradually made 
up of materials derived from that beach did not necessitate a 
north-westerly flow of the shingle ; for shingle from the old raised 
beach might have come from the eastward. The Author thought 
that the sea formerly passed between Portland and the mainland, 
and that the Fleet was part of the old shore dammed out by the 
bank. If so, why was it that the shore of the Fleet was so utterly 
unlike the neighbouring shores (of corresponding material), as 
would be seen from the map? The outline was meandering, there 
was little cliff along it, and the cliffs that existed were only a few feet 
'high ; whereas, on the coast to the west there were tolerably bold 
and straight cliffs only breached by valleys coming down to the Pvel 
of the sea. Moreover, how was the damming between Portland and 
the mainland accomplished? Some years ago his colleague, Mr. 
Bristow, and himself tried to explain the occurrence of the Fleet in 
a different manner;' and Mr. Harrison's remarks seemed to show 
that other persons had entertained similar ideas. They supposed 
that originally the Chesil Beach Avas banked up more or less against 
the land, and that in the rear of it streams came down. Farther 
west than the Chesil Bank at present stood, there were small 
streams of the same sort, which, on reaching the shingle, did 
not go through, but turned eastwards in its rear ; and they ima- 



Vide "Geol. Mag.," vol. vi., i>. 4133. 



ON THE ORIGIN OF THE CHESIL BANK. 41 

gined that the streams behind the bank, which were nearer together 
than those on the west, having a like tendency to turn eastward, 
after getting to the shingle, joined, and wore awa}' the coast in the 
rear, aided, when the water became tidal, by the tide. They 
thought, further, that the denudation of the land north of Portland, 
and north of the Chesil Bank, was more or less aided by the beds 
being there thrown in the form of an arch, which made them more 
ready to yield. It was remarkable that the channel in the rear of 
the Fleet ended just where the streams ended. Where there were 
no streams the beach was against the land; where there were 
streams the beach was divided from the land. This, so far as he 
knew, was the only case of such a beach joining land to land. 
There were plenty of beaches almost as long and jutting out far 
into the water. On the Suffolk coast they were as strongly marked 
as anywhere, but they did not join land to land. The Astronomer 
Royal appeared to feel some difficulty as to the Chesil Bank being 
formed of the old shingle ; but when it was remembered that the 
old beach must have stretched across the bay, there would be no 
difficulty in the matter of quantity ; the little beach left at Portland 
was a mere indication of what once existed. The next nearest 
piece was at the western horn of Torbay, but the same beach must 
have extended across from one point to the other. The Astronomer 
Royal seemed to think that this was the first notice of the raised 
beach ; but the Author had given full references to others who had 
described it. The first notice of it was twenty-five years ago, on 
the Geological Survey map, by Mr. Bristow. It was not thereon 
called a raised beach, but the presence of stone and conglomerate 
on that spot was marked, and it was noticed soon afterwards by a 
local geologist, who described it, though shortly, as a raised beach. 
The first more lengthy account, though still a short one, was pub- 
lished by himself. With regard to the shingle at Landguard 
Common, he had lately come from that locality, having been 
engaged on the Geological Survey in Suffolk. He had not made 
detailed investigations of the accumulation of the shingle, because 
that had been done some years ago by Mr. Eedman. The shingle 
advanced in one part, and was taken away in another ; and a 
cemetery and martello tower had been swept away, the part on 
which the}' stood (shown on the Ordnance map as a slight outward 
growth) having been cut in to such an extent as to give enough 
shingle to account for the extra beaching up at the horn at Land- 
guard. As to the supposition that shingle was washed out from 
pebble beds below the London Clay, he could answer the Astro- 
nomer Royal with some certainty. If the beds below the London 



42 MINUTES OF PROCEEDINGS. 

Clay, to which he referred, occurred under the sea, they would 
not produce the shingle at Landguard Fort ; because all the flints 
in them were rolled, there being scarcely one in a million that was 
not absolutely rounded. The actual beach at Landguard did not 
consist wholly of pebbles ; there were more or less subangular 
flints, flints in all stages of rolling to the perfect pebble. But he 
would go further, and say that the pebble beds in question did not 
exist there ; the beds between the London Clay and the Chalk at 
that spot had hardly a pebble in them : their character was known 
from well sinkings, of which there were several, at Walton, Dover- 
court, Harwich, and elsewhere, and the outcrop was not far off. 
He thought that the cliffs themselves in the neighbourhood con- 
tained material that would certainly help the formation of the 
beach. Thus at the bottom of the Crag there was a bed containing 
large unrolled flints, each of which, when broken up, as it would 
be by denudation of the coast and the action of the waves, would 
famish shingle: there were also in it flint-pebbles ready made, 
and other rocks besides, with tolerably hard phosphatic nodules, 
which were picked up along the whole of the coast. In the Crag 
there were occasional gravelly beds, and above it sand with more 
or less gravel in it. So that on the spot itself there was material 
to furnish beach, and he saw no reason for going down to a greater 
depth to find it. He was unacquainted with the district farther 
north, but he had no doubt that it furnished a great part of the 
materials of the Felixstow beach. He should like to know whether 
it was an ascertained fact that the sea at a considerable depth could 
root up shingle and push it on to the land so as to form beaches. 
He had not seen any definite proof that such could be the case, but 
he was not prepared to deny it. 

Mr. REDMAN wished to mention a few facts which had not been 
referred to either in the Paper or in the discussion. The sea- 
shore 'alluvion' in question (if it might be so termed) had 
very early attracted attention, and no beach had been more 
graphically or particularly described. It was laid down with 
great accuracy in early manuscript maps, and in a remarkable 
series of drawings collected by the great Cecil, well known 
at the British Museum as "Lord Burleigh's Book." Also by 
Collins and Lilly. There was one feature in those maps which 
showed the occurrence of a change. The Fleet, two or three 
centuries ago, was much wider than at present. That might 
lead to the inference that the beach had retreated landward ; 
but it was clear, upon a close inspection of the Chesil Beach, thai 
such was not the case. The constant accumulation of material 



ON THE ORIGIN OF THE CHESIL BANK. 4o 

upon the summit grew with the beach : the larger material, driven 
to the summit, passed over the crest and formed a long slope land- 
ward, tailing over towards the Fleet, and that constant accession 
of material had from year to year narrowed the area of the Fleet. 
The very name of the formation showed its antiquity. Leland's 
description of its characteristics and of the winds that affected it, 
and caused the withdrawal of the shingle, was as apposite now as 
when it was written, three hundred years ago. The appendage 
of the Fleet behind the Chesil Bank had been alluded to by Mr. 
Whitaker, in the Paper he had mentioned, and Sir Charles Lyell 
had done the same, and both referred to it to show what might 
have been the original formation of the Chesil Bank, — a spit of sand 
diverting the water of the rivers and forming the nucleus of the 
bank. This was characteristic of all the southern formations 
between the Chesil Bank and the Thames. At Shoreham the beach 
deflected the waters of the Adur, and inclosed a belt of water, 
with a fluctuating opening until rendered permanent by the piers 
of Chapman. Langley Point, to the east of Beachy Head, was 
formed upon a nucleus to the windward of Pevensey Harbour, the 
shingle being derived from the denudation of the beach upon 
which Old Brighton stood in the time of Elizabeth below the cliff. 
The subsequent denudation of Pevensey, travelling to the leeward, 
increased Dungeness, which was formed upon a similar spit over- 
lying the waters of the Pother up to Appledore, that great estuary 
being closed by Dungeness. A similar operation might be observed 
in the extension of beaches past Dover and Deal to Peg well Bay, 
diverting the waters of the Stour, and having almost extinguished 
the haven of Sandwich. Also upon the eastern coast at Orford, 
where the shingle deflected the land water to the extent of 10 
miles ; and at Landguard, threatening the destruction of Harwich 
Harbour. So that the Fleet was a natural appendage of the Chesil 
Bank. But there were two characteristics of that beach not 
observed in the same degree in other formations — the remarkable 
gradation of material, and the enormous height of beach at the 
leeward end. The gradation of material undoubtedly showed the 
leeward motion to be from west to east. The elevation at the 
eastward end was four times the altitude above high water of 
beaches generally. The usual height above high water at spring 
tide was from 8 feet to 10 feet; but the Chesil Bank at the Port- 
land end was 35 feet above high water at spring tides. It also 
presented another noticeable feature. Beaches usually had two 
sets-off, one marking the high water, neap tide, and the other 
the high water, spring tide. On the Chesil Bank there was an 



44 MINUTES OF PROCEEDINGS. 

enormous accumulation of material forming a third plateau, 35 feet 
above high water, spring tide. Some remarks had been made as 
to the reason why the large stones travelled to the top. bn- 
doubtedly the largest shingle travelled to leeward, and also to 
the greatest altitude. Two reasons were given, and he thought 
there was truth in each of them. The real reason why large 
shingle attained the summit of a bank had been explained on 
several occasions, namely, that the greater weight and force of 
the wave falling upon the shore drove material of all sizes up 
the slope, and in the recoil the material was drawn down in a 
regularly graduated scale, the finer material falling towards the 
bottom of the slope, the coarser being left higher on the slope] 
and the heaviest highest of all. The progressive motion of the 
beach to leeward was described by Mr. Palmer forty years ago, 
and also by Colonel Sir William Eeid. 1 Both those authors, who 
were entitled to great respect, showed that the reason why shingle 
travelled to the leeward was, that stones advanced in a series of 
right-angled triangles, the base of which was the line of the shore ; 
the rectangular side was the line of recoil of the beach falling upon 
the slope, and the hypothenuse was the diagonal course of the 
shingle, driven xip the slope by the south-west winds. That also, 
connected with the larger pebbles being left at the top of the beach 
by the weaker force of the recoil, accounted for the progressive 
leeward motion, and for the shingle attaining the greatest altitude. 
But it did not explain why the shingle passed over that enormous 
crest 35 feet above high water. In heavy gales of wind he- 
thought that the large pebbles must be looked upon as projectiles, 
and the distance they travelled as being dependent upon their 
cubical capacity together with the momentum acquired, as was 
ingeniously explained by Mr. Bramwell. "With regard to the 
travelling of the shingle to the north-west, that point was ad- 
vanced by the Astronomer Royal, in the course of a discussion on 
a Paper upon " The East Coast," and the Author had quoted the 
Astronomer Royal's opinion in support of that theory. He re- 
frained, however, from stating the opinion of such men as Sir John 
Rennie, Sir John Hawkshaw, Mr. Charles Hutton Gregory, and 
others diametrically opposed to th^se conclusions. There were time 
reasons fatal to the position taken. Supposing there were a motion 
from the south to the north-west, two results would follow, which 
did not take place. One of those was pointed out by Mr. Whitaker. 



1 Vide Papers on subjects connected with the duties of the Corps of Royal 
Engineers, vol. ii., p. r_'S. 



ON THE ORIGIN OF THE CHESIL BANK. 45 

If the beach travelled in that direction there would be a large 
amount of the largest material heaped up in the centre of the bay, 
where the greatest altitude would be attained, and this was not the 
case ; on the contrary, the largest pebbles and the greatest altitude 
were at the Isle of Portland. Both conditions showed that the 
motion was in the contrary direction, as assumed b} T Sir John 
Coode, viz., from west to east. There was the third objection, that 
the winds, to produce a travel of the beach to the north-west, 
exercised a baneful effect on the banks, and did not accumulate, but 
dissipated the material. At Dover Bay, on which he had reported 
on several occasions, the shingle was driven up much in the same 
way. There was not the same gradation of material, but there was 
(in a degree) the same extraordinary elevation. There was no 
doubt that the beach, under certain conditions, travelled in a dif- 
ferent direction, because it was pointed out both by Sir John Coode 
and by Sir William Beid, that the general leeward motion did not 
resume its eastward progress until near Osmington, and the travel 
of the beach in Weymouth Bay was in a contrary direction. Under 
certain conditions the travel of the beach was reversed in conse- 
quence of a change of weather. He had found that to be the case 
in the Deal district. It appeared from statistics furnished by 
various bodies. \\ ith regard to the winds extending over a period 
of ten years, it appeared that for four or five years prior to a report 
made by him on the subject, there had been an unusual amount 
of easterly wind, which accounted (combined with other causes) for 
the great degradation of beach, which had produced also a contrary 
movement. The influence of Portland on the tides was shown by 
the increase of range west of the island. Thus at Chesil the range 
of spring tide was 10 feet, at Wej^mouth and Portland breakwater 
7 feet. The submarine ledge of oolitic rock at the extremity of the 
island, | mile long by ^ mile wide, had gravel at its base on the 
west side, but not on the east side ; which showed that the shingle 
did not pass it. 

Mr. J. N. Douglass remarked, through the Secretary, that his ob- 
servations on the travel of shingle along the shores of England 
and Wales, extending over many years, led him to differ from 
the Author in the opinion that the material of which the 
Chesil Bank was composed had come from the eastward. The 
travel of the shingle was, he thought, chiefly due to the effects of 
the ocean wave or ground-swell. The result of this was found in 
the North Sea to be the transport of material to the southward. In 
the English and Bristol Channels material was transported to the 
eastward, and in the St. George's Channel, from its entrance 



46 MINUTES OF PROCEEDINGS. 

northerly to Holyhead, material was transported to the north- 
ward. True, the travel here indicated was in each ease subject to 
frequent checks, and the movement was often reversed by adverse 
winds and waves; nevertheless the general direction was as hi 
had stated. Now, on referring to the position of the Chesil Bank, 
and the direction of the ground-swell crossing Lyme Bay toward! 
it, as it did from the direction of the Start Point, it appeared to 
him impossible that the general travel of shingle along the bank 
could be other than south-easterly. If the raised beach at Port- 
land had extended westerly across Lyme Bay, as suggested by the 
Author, he thought that a large portion of it must have been 
transported to the Chesil Bank. He quite agreed with the opinion 
expressed by Mr. J. T. Harrison, that the beach had been largely 
supplied with material from the bottom of the bay ; indeed, he 
considered it quite possible that a portion of the supply had been 
transported from positions westward of the Start. There was 
abundant evidence in the numerous shingle banks in deep water 
around the coast of the movements of coarse sand and shingle at 
greater depths of water than were to be found in Lyme Bay ; and 
so near as the Start Point, in the probable direction of the travel of 
shingle to the Chesil Bank, was the Skerries Bank, composed of 
gravel and shingle, with 22 fathoms of water along its outer edge. 
He had been informed by fishermen at the Land's End, that their 
lobster pots were frequently filled with coarse sand and shingle 
during heavy ground-swells in depths of water up to 30 fathoms, 
some of the stones weighing as much as 1 lb. He might also 
mention that at the Bishop Lighthouse, on the westernmost rock of 
the Scilly group, coarse sand had been thrown during heavy storms 
from a depth of 25 fathoms at low water on to the lantern gallery, 
which was 120 feet above low water. 

Mr. F. WYNNE observed, through the Secretary, that a simple 
oscillating wind-wave, which advanced the largest pebbles it could 
stir farthest, because of the greater power these had of anchoring 
themselves against the backw T ask, had only a local effect, and 
the limits of its action would be nearly contour lines, one the 
height on shore to which the waves could move such pebbles, and 
the other the depth to which it could stir them. Then- wad 
another form of wave whose effect was different, and the action of 
such a wave on solid bodies had been described bj' Mr. J. Scott 
Eussell. 1 An oscillating wind-wave which affected the particles 



1 Vide " Report of the Fourteenth Meeting of the British Association for the 
Advancement of Science, 1844," p. 373. 



ON THE ORIGIN OF THE CHESIL BANK. 47 

of water in a degree rapidly diminishing with increase of depth, 
was, under certain conditions, changed into one of translation only, 
in which the motion was all in the same direction, and the 
extent of the transference was equal throughout the whole depth. 
This change took place where the slope of a beach was uniform 
and very extended. Portland was exposed during certain winds 
to the full swell of the Alantic rollers. To such rollers the 
gradual slope from the Atlantic into the comparatively shallow 
waters of the English Channel was as a shelving beach to local 
wind-waves. The Atlantic rollers if big enough might become 
waves of translation in the Channel. The force of such waves 
of ti-anslation was prodigious, and an idea of their quarry- 
ing action on a submerged reef of rock exposed to their action 
might be found, by remembering that one only 1 foot high gave a 
movement of translation of more than 5 miles an hour, while one 
of the hitherto observed maximum height of 36 feet, though, of 
rare occurrence, gave a translating movement of more than 30 miles 
an hour. The materials transported bj 7 such waves would be 
placed in the order in which they occurred on the Chesil Beach, 
the largest pebbles nearest their origin, and the others according 
to their size, farther away from it. While agreeing generally in 
what the Author said of the formation of the Chesil Beach, he 
took exception to the statement that " the one thing wanting in 
support of Sir George Airy's argument was the presence in Portland, 
or in the adjacent sea, of beds which could furnish the particular 
pebbles characteristic of the Chesil Bank." He would rather 
urge that the occurrence of any sort of rock as a pebble on that 
beach proved the existence of a more or less exposed reef of that 
rock between the commencement of the shallow water of the 
Channel and this beach. If syenite was found, then syenite existed 
in the bed of the Channel, perhaps as far as the entrance to the 
Bay of Biscay. The Chesil Beach probably represented a very small 
fraction of what was torn off and transported by these forces ; more of 
it was probably represented by the quantities of shingle known to 
pass every year through the Straits of Dover and accumulate in the 
North Sea. That large masses of shingle were displaced at Chesilton 
by great storms from the south-west was a fact, as the following 
experience would show : — A Spanish galleon was known to have 
gone down oif Chesilton many years ago, and since then, after heavy 
storms, ingots of silver were sometimes washed up at Chesilton. 
About the year 1860, several ingots shaped like quoits were 
thrown up by the same storm, which he was informed lifted a sea- 
going ship right over the beach from the West to the East Bay. 



48 MINUTES OF PROCEEDINGS. 

The existence of the Fleet indicated, he thought, a time when 
the soft materials which composed this part of the coast were 
being slowly worn down into a shallow sea by the action of local 
oscillating waves, whose action might be compared to that of a 
vertical millstone, and before the present order of things obtained 
by which the Chesil Bank was heaped up in front of the old coast 
line, acting as a bar and protection against its further degra- 
dation. 

Sir John Coode observed, through the Secretary, that he re- 
garded the present communication as a challenge, if not a denial, of 
the accuracy of the views and propositions as to the travel of the 
shingle in the AVest Bay laid down in his Paper on the Chesil Bank, 
read in 1853. He was not prepared to withdraw a single sentence of 
his original Taper ; on the contrary, the views therein expressed 
had only been strengthened by subsequent observation. There was 
one point in that Taper noticed by Trofessor Prestwich to which it 
might be well to advert, in order to remove what appeared to be a 
misapprehension as to the movement of shingle in depths of from 
6 fathoms to 8 fathoms. The facts were such as to show con- 
clusively to his mind, that the movement had been no more than 
was due to a limited rolling, during heavy gales, of the shingle 
which previously existed there, and not to fresh shingle brought 
in. One important point had come under his observation a few 
years since, viz., the tremendous transporting power which came 
into play upon the shingle on the long stretch of beach between 
Bridport and Portland during the prevalence of the heavy surf fol- 
lowing the subsidence of S.W. gales. By a series of observations in 
the locality, extending over several years, he had ascertained that of 
every eleven heavy S.W. gales, ten terminated T>3 r the wind ' flying 
up' rapidly by W. to N.W. and N.N.W., and then subsiding. This 
state of things always resulted in the changing of the direction of the 
breakers near the shore, and so deflecting them in a distinct south- 
easterly direction, as to drive the shingle along the coast from J 
Bridport and Burton towards Portland. He was indebted to the 
Author for affording him the opportunity of bringing this re- 
sult of comparatively recent observation thus prominently under 
the notice of the Institution. The Author and the Astronomer 
Royal had entirely ignored the facts, ascertained after lengthened 
inquiry for the purposes of his Paper of 185)!, and, as it appeared 
to him, without sufficient grounds, attempted to disturb what Lad 
been then regarded as established conclusions, as to the laws which 
governed the movements of shingle, not only in the West Bay, but 
also on other parts of the coast. It would have been more logical 



ON THE ORIGIN OF THE CHESIL BANK. 49 

either to have disproved the facts therein stated, or to have 
produced others of a more convincing and adverse character, 
before denying the conclusions upon which those facts were based. 
He yielded to no one in his respect for the high attainments of 
the Astronomer Eoyal, and a sense, of the great services rendered 
by him fo the country and to the cause of science generally. 
Differing, however, essentially from the Astronomer Royal upon 
this subject, he felt bound to express his adhesion to the views 
contained in the Paper read upwards of twenty years since. In 
the discussion upon Mr. Eedman's communication on the East Coast 
in 1864, the Astronomer Eoyal stated that he found himself in a 
difficulty with regard to the theory laid down in the Paper of 1853, 
remarking that " being in this difficulty, he must be forgiven if he 
made a strong supposition," and "the only conclusion he could 
come to was this : that' the materials which formed that bank 
were piled up by the sea ; that they had been torn up by the 
violence of the surf from the bottom of the sea ;" adding that " he 
was obliged to attach to this the additional supposition that in that 
part of the bay under Portland there were strata which furnished 
those coarse blood-stones, which had caused the difficulty." The 
Astronomer Eoyal, on that occasion, mentioned, by way of illustra- 
tion, in confirmation of his views, two cases where the conditions 
were totally different from those in the West Bay ; he quoted Wex- 
ford Harbour and the Mersey, but in each of these instances the tide 
rushed through a comparatively narrow gorge to fill areas comprising 
many thousand acres within, the material scoured being fine sand ; 
whereas the Chesil Bank was situated within one of the largest bays 
in the kingdom, the distance from headland to headland being about 
60 miles, and the depth from the chord-line being nearly 25 miles. 
As regarded the " supposition " that the materials had been torn up 
by the violence of the surf from the bottom of the sea, it was 
manifest that the Astronomer Eoyal must have greatly changed 
his views since 1845, when he presented to the Commissioners on 
the formation of a Harbour of Eefuge at Dover a summary of the 
points on which he was willing to offer them an opinion. That 
summary contained the following : — 

" (6). The tidal current is the only motion which can affect 

the shingle in deep, or moderately deep, water. 

" (7). Because the motion of waves is insensible at the bottom 

of deep water (the motion diminishes very rapidly with the 

depth). 

" (8). In deep water, the tidal current operates equally in 

opposite directions. 
^1874-75. n.s.] E 



50 MINUTES OP PROCEEDINGS. 

" (9). On the whole, it is very unlikely that the shingle is 
sensibly moved at the depth of a few feet." 1 
The essence of the Paper consisted in the endeavour of the Author 
to show that he had discovered " the one thing wanting in sup- 
port of Sir George Airy's argument," viz., " the presence in Port- 
land, or in the adjacent sea, of beds which could furnish the 
particular pebbles characteristic of the Chesil Bank ;" referring to 
the fact that the raised beach of Portland Bill had not been noticed 
in 1853. However, the Astronomer Royal declined to accept Pro- 
fessor Prestwich's views in this respect, remarking, what would 
seem to be obvious, that " he could hardly imagine that there 
would have been materials enough at that place to account for the 
formation of the whole of the bank." If the Astronomer Royal's 
views as to the origin of the shingle were correct, it would appear 
impossible to account for the existence of the " Shambles," an 
immense bank of fine broken shells lying south-east of Portland, 
which was now in the same condition as when surveyed by Mac- 
kenzie, about one hundred years since, and having now, as then, a 
depth of only 1 1 feet of water over the crest. If the Astronomer 
Royal's theory were correct, the whole of this bank would assur- 
edly be torn up by the first southerly gale, and the materials be 
landed on the beaches upon the east side of the island of Portland ; 
and similar banks of sand or gravel lying off different parts of the 
coast — the Goodwin Sands, for instance — would cease to exist after 
an easterly gale ; their materials would be torn up and thrown 
upon the coast between the North and South Forelands. As a fur- 
ther example, the great banks lying to the eastward of Yarmouth 
would disappear after the first north-easterly gale, and their 
materials would be thrown upon the coast to leeward ; in short, the 
Admiralty charts of such localities would be altogether valueless. 
He would now deal seriatim with the several points comprised in 
the summary of the Paper, with the view of showing that the 
facts were opposed to the conclusions. First, as to the derivation of 
the shingle, the Admiralty charts certainly did not confirm the 
Author's view. The bottom immediately beneath and seaward of 
this "raised beach" was described in the "Channel Pilot" as "a 
remarkable shelf of rock called Portland Ledge, extending a mile 
in a south-south-westerly direction from the pitch of the Bill, and 
terminating in a sharp point ;" the bottom, where marked on the 



1 Vide Report on the Harbour of Refuge to be constructed in Dover Bay. 
Appendix to the Minutes of Evidence, p. 80. London, 184b'. 



ON THE ORIGIN OF THE CHESIL BANK. 51 

chart, consisted of " rock " and " shells." To the Author's second 
proposition it might be answered, in the first place, that the exist- 
ence of similar shingle to that in the old beach in the bed of the 
Channel had first to be proved ; the absence of it had just been 
shown by reference to the Admiralty chart. He had already 
stated that the travel of the waves during heavy storms was 
turned from south, around by west, to north-west, and therefore 
precisely in the opposite direction to that which the Author 
asserted as the run of the shingle. Respecting the tidal current, 
the following quotation was from " The Pilots' Handbook for 
the English Channel," compiled by Staff-Commander I. W. 
King, R.N., late of the Admiralty Hydrographic Office : — " There 
is an outset from the West Bay on the north-west side of Port- 
land, of nearly nine hours' duration, which closely skirts the 
rocky shore and gradually increases in strength as it approaches 
the Bill, where it acquires such velocity as to extend far beyond 
that point before it turns to the east." This strong outset for 
nine hours out of twelve was in a diametrically opposite direction 
to that stated by the Author of the Paper. As to the shingle- 
currents from opposite directions meeting at Burton Cliff, the 
obvious objection was that there was no such heaping up of 
shingle at that point as would necessarily follow if the Author's 
views were correct. The Author's third proposition had already 
been sufficiently answered in the remarks under the last head. 
With regard to the fourth proposition, the small piece of " raised 
beach" at Portland Bill might undoubtedly have been derived 
from the coasts of Devonshire and of the south of Dorset, under 
different geological and physical conditions, but this would prove 
nothing whatever adverse to the views adduced by him in 1853, 
but rather the contrar}^. The fifth point, viz., " that the sea for 
a time passed between Portland and Weymouth," seemed to be 
foreign, or at any rate not material, to the questions of the origin, 
or travel of the shingle, of the Chesil Bank. In regard to the 
Author's sixth proposition, no question could well arise as to the 
accuracy of the general statement of the old beaches and gravel 
having contributed to the formation of the existing beaches ; this, 
however, did not militate against the conclusions he had previ- 
ously arrived at. In further corroboration of his views, it might 
be stated that rather more than two years since, a vessel, named 
the " Eoyal Adelaide," having on board a large quantity of iron- 
mongery, was wrecked on the Chesil Bank, about 2^ miles to the 
north-west of Portland. The bulk of this ironmongery was gra- 
dually carried along the bank to its south-east extremity under 



52 MINUTES OF PROCEEDINGS. 

Portland, and consequently in an opposite direction to the line of 
travel assumed by Professor Prestwich. This one fact seemed con- 
clusive as to the ultimate direction of the " travel " of shingle along 
the beach. 

Professor Prestwich, in reply, said an opinion seemed to prevail 
that he had contested the view generally held, that on the coast of 
the English Channel the shingle as a rule travelled from west to 
east. He did not for a moment contest that point, which he, on the 
contrary, considered had been well established by Colonel Reid, 
Mr. Palmer, Mr. Redman, and others ; but he wished to point out, 
that owing to causes which he had explained, there was a different 
action in the West Bay of Portland. Mr. Whitaker had rightly ex- 
pressed his views with regard to the extent of the raised beach. 
The remnants at Portland, Torquay, and Dartmouth showed, 
that at a former period the beach must have extended from the 
one point to the other, and that the land between these points 
had been worn away ; consequently the Portland rocks, together 
with other underlying strata, formerly stretched across Lyme Bay, 
forming a connected line to some point on the coast of Devonshire. 
What that exact line was it was impossible to say, but as the coast 
was now in constant process of being worn back, it followed that, 
at the period when the raised beach was formed, the coast must have 
been much farther advanced in the bay than it was at the present 
time — a view he was glad to find corroborated by the observations 
of Mr. J. T. Harrison. The present raised beach was a mere 
remnant — nothing compared with the portion which had been re- 
moved. This denudation was effected by the sea- wear of the coast- 
line and the removal of the softer sand and clay by tidal currents. 
The hard pebbles, flint, and chert were not destroyed. They re- 
mained scattered over the bed of the sea, after the softer strata were 
worn and washed away. Therefore he held that, somewhere in 
the area which he had pointed out, there must be the remains 
of the old beach. The materials exactly corresponded, pebble for 
pebble, only that they were much more worn, with those now 
found in the Chesil Bank, — those pebbles having travelled east- 
ward at the period when the beach extended across the bay, by the 
action of the same westerly or south-wester^ winds that now 
prevailed. He was satisfied that in that old beach there was a 
store amply sufficient to provide for the Chesil Bank. The 
Admiralty charts gave evidence of the presence of shingle over 
much of that area. The drift of the present beach was no doubt 
from Budleigh Salterton past Sidmouth to Lyme Eegis and Brid- 
port ; but there, he maintained, the easterly drift ceased, because 



ON THE ORIGIN OP THE CHESIL BANK. 53 

the quartzite pebbles from the conglomerates of Budleigh, so 
common at Sidniouth, were rare at Lyme and were hardly to be 
found at Bridport. That was sufficient to prove that the travel of 
the beach from Devonshire did not extend continuously, or in large 
quantities, to the Dorset coast. In fact the beach tailed off there 
from the westward, as it did in the other direction from the east- 
ward, for want of motive power. It was fairly objected, an objec- 
tion which had occurred to himself, that the constant travel of the 
beach in these directions should, at the point of junction, have formed 
a large beach ; but it did not do so, for the reason above mentioned, 
although there was shingle spread out in the bight of the bay which 
might be derived from that source. There was more sand at the 
Bridport end of the beach than at the Chesilton end. It had been 
asked, if the wear of the shingle has been so great in travelling from 
Portland to Abbotsbury, how was it that in the original travel 
from the Devon coast to Portland it had not been subject to the 
same wear and the same reduction? The fact was that the original 
shingle consisted of large and coarse shingle mixed ; and he believed 
that the smaller shingle at the Abbotsbury end arose, not so much 
from the wear of the shingle as it travelled westward, as to the 
sorting action of the sea in carrying the smaller shingle to the 
greater distance. The fact of large pebbles being found at the top 
of the beach was quite different from large shingle travelling 
under water. The latter action had been investigated by the late 
Mr. Hopkins, and the rate at which small and large shingle 
travelled well established; but the operation that would cast shingle 
on the beach, when it once came within reach of the wave power 
on the shore, was different from that which would transport it to 
distances under water. They were independent actions. With 
regard to the power of the winds on this coast and their particular 
direction, he was not aware of any more complete tables and re- 
duced observations of more recent date than those contained in the 
report of Sir W. Snow Harris — these also were the tables upon 
which Sir John Coode had founded his observations. • He did not, 
however, confine himself altogether to the integral force of the 
wind, but he also gave the amount of prevalent winds indepen- 
dently of any other point. The question was an extremely 
complex one. The force of the wind-wave depended primarily 
upon the force of the prevalent winds, but it was modified mate- 
rially by the position of the land. The coast of Lyme Bay was a 
good deal protected from the direct westerly winds by Start Point, 
and from easterly winds by Portland, while it was open to the winds 
from the south-west and south. But after all it was a question 



54 MINUTES OF PROCEEDINGS. 

rather of fact than of theory, and as shown in the instance of 
Weymouth Bay, to which he had alluded, the east to west travel 
of the shingle was clear. There again he believed it tailed off just 
as it reached Wej-mouth, owing to the changed direction of the 
land. With regard to the instance of Landguard Fort, he much 
agreed with the opinion of Mr. Whitaker ; but he thought there 
was another source of supply to the shingle thei - e, namely, the 
great beds of shingle, from 10 feet to 30 feet or 40 feet thick, a few 
miles to the north, in the neighbourhood of Dunwich and South- 
wold, which he had described as the Westleton pebble beds. He 
considered the shingle alluded to by Mr. Harrison, as covering 
much of the sea bed, in and off Lyme Bay, was to be attributed to 
submerged portions of the old beach, and not to submerged rocks, 
as he believed that all shingle was of subaerial origin, and he 
thought, therefore, that that now found out at sea was due rather 
to former beach or river action than to the present wear of sub- 
marine rocks. 

In discussing the subject he had not referred to the opinions 
of other speakers, which were entitled to great weight, as he took 
the opinions advanced by Sir John Coode and the Astronomer 
Royal, as representing the two sides of the question, both of which 
had their supporters. 

In conclusion, Professor Prestwich did not wish in any way to 
ignore the facts, or to question many of the conclusions respecting 
the laws which governed the movements of shingle arrived at 
by Sir John Coode. On the contrary, he accepted without hesitation 
all Sir John Coode's facts, together with those general conclusions 
relating to the travelling of the shingle, governed by the preva- 
lence of certain winds; but while he accepted that law, he ventured 
to question the resultants in this particular instance. The easterly 
travel of shingle, under the influence of westerly and south-westerly 
winds, along a coast trending east and west, he treated as esta- 
blished. But the southward trend of the coast formed by the Isle 
of Portland altered the conditions ; and as the Chcsil Bank ranged 
almost due S.E. and N.W., it became a nice question as to which 
point of the prevalent winds had hero the greatest effect. AYhile 
Sir John Coode took the mean of S.W. -h W. as the direction of the 
greatest wind-force, he considered it to be a little more south, viz., 
8.S.W. The difference was not great ; but it was just sufficient to 
turn the balance. He would be glad to see some practical deter- 
mination of it. With regard to the "Royal Adelaide," the Author's 
information did not agree with that of Sir John Coode as to the 
exact position of the wreck. He was informed, on the best au- 



ON THE ORIGIN OP THE CHESIL BANK. 55 

thority, that it took place rather more than \ mile on the Portland 
side of the Ferry Bridge, or 1 mile 640 yards from the Portland 
railway station ; and he could not ascertain that there was any 
reliable evidence of the drifting of the heavier portions of the 
cargo in either direction. With respect to the lighter things, they 
would be caught by the first heavy wind and blown over the 
summit of the Bank, where they would be sheltered under its lee 
from westerly winds. With regard to the Astronomer Eoyal's 
observation, that he could not accept the Author's views in 
one respect, as he could hardly imagine there would have been 
material enough at Portland Bill to account for the formation 
of the Bank — that observation was evidently made under a mis- 
apprehension, as Professor Prestwich never intended to imply that 
the whole materials of the Chesil Bank were derived from the 
" raised beach " at the Bill, but, on the contrary, that they were de- 
rived chiefly, if not wholly, from the bed of the sea, for some miles 
westward of the Bill — in the position, in fact, of the supposititious 
strata of Sir George Airy. It was evident that if the " raised 
beach " at the Bill and that at Torquay represented parts of one 
whole beach, that whole must have been once continuous, just as 
much as the beach was now continuous from Hastings to Dover, 
and that the wreck of the intermediate portions must lie at the 
bottom of the sea, which now covered the ground it once occu- 
pied. The presence of shoals and sand-banks was no proof of the 
absence of eroding power in tidal currents under the influence 
of storms ; but it only showed that counteracting causes, such 
as currents or eddies, interfered with their local action. No 
doubt the scour of the tidal current off the Bill of Portland 
kept the ledge free of gravel ; but it did not prevent its lodging 
in the deep water at its base. Indeed the Admiralty Chart marked 
gravel in four soundings on the western side of the ledge. And, 
besides indicating a gravel bottom in various soundings be- 
tween this spot and Lyme Bay, it was stated in the " Channel 
Pilot" (4th ed., p. 124), that the West Bay of Portland, where 
the water was deep, " cannot be recommended as a safe anchorage 
for large vessels; for, should the wind suddenly change to the 
westward, a heavy sea soon gets up, and the holding-ground is 
bad, being loose gravel or shingle." The same authority also 
stated that " the incoming tide, or outset, from the West Bay of 
Portland, runs (for about nine hours) closely skirting the rocky 
shore, and gradually increasing in strength as it reaches the Bill, 
where it acquires such velocity as to extend far beyond that point 
before it turns to the eastward. ... A short distance eastward of 



f)6 MINUTES OF PROCEEDINGS. 

the ledge this outset is met, in the latter half of its course, at 
nearly right angles, by the stream which sets for nine and a half 
hours out of the East Bay of Portland" (p. 140). Farther on 
it is stated that " the reverse of the foregoing remarks is also 
applicable to the course of the outgoing or -western stream." 
'• From the north-east end of Portland it rushes furiously round 
Godnor Point towards the Shambles and (westward) past the Bill." 
Any shingle, therefore, in the channel of this race would be driven 
backwards and forwards until thrown up by some other determin- 
ing cause. In the West Bay and in Lyme Bay the tidal current 
became so slight as to be inoperative, except probably for the 
transport of silt and sand. The Author admitted the apparent 
difficulty — that the opposite direction of the shingle currents near 
Bridport had caused no heaping up of the shingle at that point ; 
but, on the other hand, he would observe that if the shingle moved 
all in one direction, or uninterruptedly from west to east, there 
should be no break in the continuity of the beach from Budleigh 
Salterton to Portland ; whereas such a break did occur off Bridport, 
— the stream from Devon thinning off gradually as it approached 
from the westward, and the stream from Portland thinning off as 
it approached from the south-eastward, while the intermediate 
strand consisted chiefly of sand. The case would be different 
if either of these streams were intercepted by groynes, against 
which the shingle would necessarily accumulate ; but here, meet- 
ing with no impediment, they gradually thinned out, and would 
do so until, in the process of time, they met. With refer- 
ence to the Fleet, it was introduced solely as a corollary to the 
formation of the Chesil Bank, as a consequence which could hardly 
be avoided; but he had abstained from discussing the general 
questions connected with it, as foreign to the object of the Paper. 
He would point out, however, that, so far from there being any 
material difference in the shores west and east of the Weymouth 
promontory before the formation of the present beaches, the shore 
from Wyke to Abbotsbury was not dissimilar to that which ob- 
tained from Weymouth to Preston. Nor did his remarks intend to 
apply to the relative size of the stones on the top or on the slopes 
of the bank, but merely to the general size of the pebbles form- 
ing the whole mass of the bank at either end of it. This regular 
decrease he could not but attribute partly to the wear, but still 
more to the sorting and longer travel of the smaller shingle from 
south-east to north-west ; and while that direction of travel coin- 
cided with that of the suggested origin, pebbles from the old " raised 
beach," he did not see how otherwise to account for the presence, in 



ON THE ORIGIN OF THE CHESIL BANK. 



57 



the Chesil Bank, of oolite and oolitic flint pebbles derived from the 
Portland beds ; for the other tract of these strata, which passed by 
Lulworth to Upway, did not extend westward beyond Portisham, 
and did not therefore touch the coast between Portland and 
Bridport. The only alternative that occurred to the Author was 
that there might be little lateral movement of the beach, and that 
the pebbles were carried under water to distances in accordance 
with their size, and were cast up along the whole line in accor- 
dance with the force of the waves — both the transporting wave- 
power and the projecting wave-power decreasing, as before men- 
tioned, in proceeding from the south-east to the north-west. A 
series of dredging experiments would throw much light on the 
question. Since the reading of the Paper, a curious case affecting 
the distribution of shingle over the bed of the Channel had come to 
his knowledge. Dr. Bowerbank drew attention (" Hastings and 
St. Leonards News" of April 15th, 1870) to the quantity of 
shingle removed from the beach at Hastings by the fishing boats, 
and calculated that as there were fifty-three, each boat requiring 
about 4 tons weekly, the quantity annually abstracted amounted to 
11,000 tons. Now, this in a century would amount to 1,100,000 
tons, or more than enough to cover a square mile to the depth of 
1 foot. Considering the time that this had been in operation, and 
the number of fishing ports on both sides of the Channel at which 
this took place, the quantity of shingle which had thus been dis- 
tributed over the fishing grounds in the Channel could not be in- 
considerable, and showed that there were other than natural causes 
to be kept in view, and that the in-drift of the shingle was probably 
an element almost as important as its easterly shore-drift. 



February 9 and 16, 1875. 

THOS. E. HARBISON, President, 

in the Chair. 

The discussion upon the Paper, No. 1,403, " On the Origin of 
the Chesil Bank, and on the Eelation of the existing Beaches to past 
Geological Changes, independent of the present Coast Action," by 
Professor Prestwich, occupied the whole of these evenings. 



[1874-75. N.s.| 



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